Rewrite Makefile, trying to make it a bit cleaner. Tweak related files.
- Add support for cross-compiling, by setting TARGET on command line.
- Drop support for Cygwin 1.5.
- Add support for 64-bit Cygwin (i.e. x86_64-pc-cygwin).
- Generate version string automatically.
- Commonalise code for creating zips.
- Drop bz2 target.
- Avoid complaints about missing dependency files.
- Document targets and command line variables.



git-svn-id: http://mintty.googlecode.com/svn/trunk@1298 2782a51e-c42b-11dd-927d-974589228060