Merge branch 'msvc' into msvc-for-1.11

Merge branch 'msvc' into msvc-for-1.11

* msvc:
  tests: various minor tweakings, mostly related to AM_PROG_AR
  maint-mode: fix botched configure messages
  tests: few improvements to some `ar-lib' related tests
  warnings: new 'extra-portability' category, for AM_PROG_AR
  ar-lib: new 'AM_PROG_AR' macro, triggering the 'ar-lib' script
  Skip MSVC oriented tests if the shell is not capable.
  Fix latest ChangeLog entries.
  lib/compile: update scriptversion.
  compile: clear the `eat' variable earlier.
  depcomp: add new one-pass depmode for MSVC 7 and later.
  tests: fix ar-lib.test for echo that interprets backslashes.
  compile: implement library search to support MSVC static linking
  Make ar-lib support backslashed files in archives.
  Do file name conversion for object files in the compile wrapper.
  Optimize compile script on MSYS.
  Support more C++ file extensions for MSVC in the compile script.
  Enable the use of "link -lib" as the wrapped archiver.
  Add new auxiliary 'ar-lib' script, wrapping Microsoft lib.
  Fix shell pattern negation in compile script.
  Wrap some MSVC options in the compile script.