We shouldn't need it, as we don't call cygwin's gcc, and it was causing
problems with the nightly builders passing it to GHC.

Fixes trac #1971: unjustified warning about documentation

Before telling the user to add it, when installing a bindist, check to
see if $(bindir) is already in the path.

- This image is in the public domain, cf 
  http://en.wikipedia.org/wiki/Image:Greek_lc_lamda_thin.svg

- Also moving all MacOS-specific Makefile components into 
  distrib/MacOS/Makefile

- GHC as a Mac framework
- I tried to make a package where the user could choose whether to install
  in /Library/Frameworks or ~/Library/Frameworks (to allow installation for
  non-admins).  However, that doesn't work well without including the whole
  distribution twice as the decision as to whether the admin password needs
  to be entered is made at packaging time (not at install time).

configure will set INSTALL to ./install-sh if it can't find it in the path,
so we need to replace the . with the path to our root.

Patch from Christian Maeder

MERGE TO STABLE

We have 4 new flags:

  -fno-gen-manifest
     suppresses creation of foo.exe.manifest

  -fno-embed-manifest
     suppresses embedding of the manifest in the executable

  -pgmwindres
     specify a program to use instead of windres

  -optwindres
     extra options to pass to windres

"windres" is now copied from mingw and included in a binary
distribution.