Add dependence arc from running rustc to its libraries.

This commit fixes some oversights in the Makefile where rustc could be
invoked without some of its dependencies yet in place.  (I encountered
the problem in practice; its not just theoretical.)

As written in Makefile.in, $(STAGE$(1)_T_$(2)_H_$(3)) is the way one
writes an invocation of rustc where $(1) is the stage number $(2) is
the target triple $(3) is the host triple.  (Other uses of the macro
may plug in actual values or different parameters in for those three
formal parameters.)

When you have invocations of $(STAGE...), you need to make sure that
its dependences are satisfied; otherwise, if someone is using `make
-jN` for certain (large-ish) `N`, one can encounter situations where
GNU make attempts to invoke `rustc` before it has actually copied some
of its libraries into place, such as libmorestack.a, which causes a
link failure when the rustc invocation attempts to link in those
libraries.

In this case, the main prerequisite to add is TSREQ$(1)_T_$(2)_H_$(3),
which is described in Makefile.in as "Prerequisites for using the
stageN compiler to build target artifacts"

----

In addition to adding the extra dependences on TSREQ..., I also
replaced occurrences of the pattern:

    TSREQ$(1)_T_$(2)_H_$(3)
    $$(TLIB$(1)_T_$(2)_H_$(3))/$(CFG_STDLIB_$(2))
    $$(TLIB$(1)_T_$(2)_H_$(3))/$(CFG_EXTRALIB_$(2))

with:

    SREQ$(1)_T_$(2)_H_$(3)

which is equivalent to the above, as defined in Makefile.in

----

Finally, for the cases where TSREQ was missing in tests.mk, I went
ahead and put in a dependence on SREQ rather than just TSREQ, since it
was not clear to me how one could expect to compile those cases
without stdlib and extralib.

(It could well be that I should have gone ahead and done the same in
 other cases where I saw TSREQ was missing, and put SREQ in those
 cases as well.  But this seemed like a good measure for now, without
 needing to tax my understanding of the overall makefile
 infrastructure much further.)
Change libaux directory to fix aux crate tests on Windows
tutorial: Repair broken links
tutorial: Fix obsolete names
tutorial: Remove the sentence about mutable fields.
Compare file:line prefix case-insensitively on win32
Paths are case insensitive on windows and rustc and compiletest may disagree on casing.
Fixes test compile-fail/circular_modules_main
xfail tests that are currently failing on windows, reported in #7999
rustpkg: Clean up usage messages for install
rustpkg: Handle non-numeric versions; some cleanup

Package IDs can now be of the form a/b/c#FOO, where (if a/b/c is
a git repository) FOO is any tag in the repository. Non-numeric
tags only match against package IDs with the same tag, and aren't
compared linearly like numeric versions.

While I was at it, refactored the code that calls `git clone`,
and segregated build output properly for different packages.
Convert uses of transmute which don't need it
libstd: Implement {peer, socket}_name for new rt tcp & udp.
libstd: Fix errors when rtdebug! is not a noop.
libstd: Handle IPv4-Mapped/Compatible IPv6 addresses.
Add a function to check whether a ValueRef is a constant
Make omission of impossible if-else branches work with constants

Until now, we only optimized away impossible branches when there is a
literal true/false in the code. But since the LLVM IR builder already does
constant folding for us, we can trivially expand that to work with
constants as well.

Refs #7834
Generate branchless code when "if" can be evaluated at compile time

We already avoid the conditional branch, but still have an
unconditional branch in the generated code. Remove it.
debuginfo: Implemented support for destructured locals.

Conflicts:
	src/librustc/middle/trans/debuginfo.rs
	src/test/debug-info/destructured-local.rs
debuginfo: Support for function arguments. (WIP)
debuginfo: Support for destructured function arguments.
debuginfo: Minor cleanup now possible with new snapshot.