Add integer multiplication based on Karatsuba's algorithm

  library/integer.m:
    Adds Karatsuba based fast integer algorithm in the function
    `pos_mul_karatsuba' which replaces the call to `pos_mul_list' in `pos_mul'.

    It is a divide and conquer algorithm which uses O(n^1.585) basic
    operations instead of O(n^2). The function expects two positive
    integer variables, the first one must have at most as many digits as
    the second one. It falls back to quadratic multiplication if the
    larger factor has less than `karatsuba_threshold' digits.

    If compiled in a parallel grade, the function uses parallelism for the
    divide and conquer part for numbers with more than
    `karatsuba_parallel_threshold' digits.

    The current values for `karatsuba_threshold' is 35,
    `karatsuba_parallel_threshold' is 10 times this value.
Re-enable executable stripping on Mac OS X.

configure.ac:
	Pass -x to strip when linking an executable against Mercury shared
	libraries on Mac OS X.

	Make the up-to-date check require {14.01.-beta,rotd}-2014-05-05
        or later.

scripts/Mercury.config.in:
	Set the default values of --strip-executable-{shared,static}-flags.
Merge pull request #13 from mgudemann/integer_arithmetic

Add integer multiplication based on Karatsuba's algorithm
Fix resource leaks in dir fold predicates.

The directory stream was not closed if dir.open succeeded in opening
the directory, but failing to read the first entry (which may be as
simple as an empty directory).

The directory stream was also not closed when dir.foldl2_process_dir2
returns an error value.

library/dir.m:
	As above.

tests/hard_coded/Mmakefile:
tests/hard_coded/dir_fold.exp:
tests/hard_coded/dir_fold.m:
	Add regression test.

NEWS:
	Announce change.
Announce recent fixes to the MinGW and MinGW64 ports.

NEWS:
	As above.
Add barriers (for concurrency) to the standard library

Mission Critical IT has maintained a library of code for concurrent
programming.  We're happy to contribute this upstream to the Mercury
project starting with this module implementing barriers.

library/thread.barrier.m:
    Add the new module implementing barriers.

library/thread.m:
library/library.m:
    Add new module.

NEWS:
    Announce the new module.

library/thread.semaphore.m:
    Add a comment.
Add a test case for barriers and fix a bug.

This test case is based off Sebastian Godelet's work, which found a bug that
can occur when release/3 is called on a barrier and then other calls to
wait/3 are made.  The final call to wait/3 tries to execute the normal
'unblock the barrier' code and deadlocks there because the barrier is
already unlocked, specifically a value is already present in the "Go" mvar.
Thanks Sebastian for your test case.

library/thread.barrier.m:
    Handle release/3 properly: release/3 now sets the number of remaining
    threads to reach the barrier to zero, and wait/3 will determine why this
    iz zero (it's normally at least one), and if it is because release was
    called then no error is raised.  The other reasion why the number of
    remaining threads may be zero is because wait has been called too many
    times, in this case wait/3 will throw an exception.

tests/hard_coded/Mmakefile:
tests/hard_coded/thread_barrier_test.exp:
tests/hard_coded/thread_barrier_test.m:
    Add new test case.

tests/hard_coded/thread_test_utils.m
    This module contains code that may be useful for other concurrency
    tests.
Added the times operator for regular expressions, such that one can express
/[a-z]{10}/ in this way: `Regex = range('a', 'z') * 10'.

extras/lex/lex.m:
    Removed unused and unsafe str_foldr function,
    added (T * int) = regexp function.

extras/lex/samples/lex_demo.m:
    Removed whitespace in comments,
    added an input prompt,
    added a lexeme for '//' C++ comments using the new '*' operator.
Fixes for lex_demo.m

lex_demo.m wasn't compiling because io.print_line doesn't exist.  I also
found that drawing the "> " prompt wasn't working as expected.  This patch
fixes both these issues.

extras/lex/samples/lex_demo.m:
    As above.
Re-enable executable stripping on Mac OS X.

configure.ac:
	Pass -x to strip when linking an executable against Mercury shared
	libraries on Mac OS X.

	Make the up-to-date check require {14.01.-beta,rotd}-2014-05-05
        or later.

scripts/Mercury.config.in:
	Set the default values of --strip-executable-{shared,static}-flags.
Fix resource leaks in dir fold predicates.

The directory stream was not closed if dir.open succeeded in opening
the directory, but failing to read the first entry (which may be as
simple as an empty directory).

The directory stream was also not closed when dir.foldl2_process_dir2
returns an error value.

library/dir.m:
	As above.

tests/hard_coded/Mmakefile:
tests/hard_coded/dir_fold.exp:
tests/hard_coded/dir_fold.m:
	Add regression test.

NEWS:
	Announce change.
Announce recent fixes to the MinGW and MinGW64 ports.

NEWS:
	As above.
Make the thread_barrier_test a conditional test.

When I added this test recently I forgot to make it condition on any grade
with a par component, or the java and csharp grades.  This patch fixes this.

tests/hard_coded/Mmakefile:
    As above.
Add an option to mandelbrot to make it easier to test parallelism

Add a --parallel command line option to the mandelbrot benchmark that can be
given to use explicitly parallelised routines.  This makes it easier to turn
on and off explicit parallelism, depending on your testing needs.

benchmarks/progs/mandelbrot/mandelbrot.m:
    As above
Merge branch 'version-14_01-branch'

Merge recent changes on the release branch into the master branch.  This
includes a couple of changes to the NEWS file plus a fix for resource leaks
in the dir standard library module.
Do not escape character strings in internal atom representation.

The internal representation of a character constant as an atom term
should not use escaped character syntax; the escaping should occur
when writing the external representation only.

compiler/hlds_out_mode.m:
compiler/intermod.m:
compiler/prog_util.m:
compiler/type_constraints.m:
compiler/typecheck.m:
	Fix instances of the bug.

tests/valid/Mercury.options
tests/valid/Mmakefile
tests/valid/intermod_char.m
tests/valid/intermod_char2.m
	Add test case.  The .opt file was invalid because the character
	in the clause head was doubly-escaped.
Merge fix for bug #330 into version-14_01-branch

Commit 5254245ae34ab6b3ca0f7dcd3c7fc807e1407f7d was inadvertently
merged onto version-14_01-branch but NOT the subsequent fix in
commit 8c72b1e5c0c23353770c494bcdf35a450ebf7c85
Create README.md

(Commit log by Paul Bone)

Github will automatically format and display a file named README.md in the
root directory of any project.  This can be helpful to, at a minimum, direct
anyone browsing github to the project's website.  Sebastian has contributed
the following README.md.

README.md:
    New markdown-formatted README file for github.
README.md changes

README.md:
    Changed intro to www.mercurylang.org introduction.

    Added a NOTES and LIMITATIONS section.

    Added a link to the README.bootstrap.
Make a number of changes to the README.md file

README.md:
    Reorder the list or README files to that they occur from most relevant
    to new users to least relevant.  In particular put commonly-used
    backends and platforms earlier in the list.

    Provide some introductory text that introduce the user to the multiple
    backends available.

    Add further links to more information such as the documentation.

    Add text so that the file reads more natrually.