Allow Literal objects to be compared among each others.

This small change allows Literal objects to be compared, so that calls like for
example AppendUnique only append one instance when string compares to True
instead of duplicated values.
Merge pull request #80, Literal objects compare for equality
Added tests for Literal object comparison, and updated CHANGES.txt.
fix for visual studio expres on win7 x86_64
(transplanted from d7e892b4978439c6374d090912f13afa13e8daf8)
fix missing file test
(transplanted from 19a5828d1523a8308cf652d18eb1824e85d1c304)
- fix for #2916, "Issues with versioned SharedLibrary under OpenBSD"
Fix http://scons.tigris.org/issues/show_bug.cgi?id=2903
Addition of warning if build doesn't build expected targets.

Added option to runtest.py to stop on first error
Added test to verify warning works and doesn't trigger for -n or aliases
Updated src/CHANGES.txt for pull req #81.
Merged pull req #85
Merged pull request #86
Added test for bug 2909, pull req #86.
From Bogdan Tenea: Check for 8.3 filenames on cygwin as well as win32 to make variant_dir work properly.
Added Pseudo command to environment and tests. If a target is declared as
Pseudo, it must NOT exist after the build rule is executed.
Fixed wrong name in tests
Fixing test failures
Allow multiple options with --debug
Merged scons/scons into default
support for --cache-readonly
Setting this will fetch data from the cache but won't update it.