Merge branch 'jh/msvc'

Merge branch 'jh/msvc'

Support to build with MSVC has been updated.

* jh/msvc:
  msvc: ignore .dll and incremental compile output
  msvc: avoid debug assertion windows in Debug Mode
  msvc: do not pretend to support all signals
  msvc: add pragmas for common warnings
  msvc: add a compile-time flag to allow detailed heap debugging
  msvc: support building Git using MS Visual C++
  msvc: update Makefile to allow for spaces in the compiler path
  msvc: fix detect_msys_tty()
  msvc: define ftello()
  msvc: do not re-declare the timespec struct
  msvc: mark a variable as non-const
  msvc: define O_ACCMODE
  msvc: include sigset_t definition
  msvc: fix dependencies of compat/msvc.c
  mingw: replace mingw_startup() hack
  obstack: fix compiler warning
  cache-tree/blame: avoid reusing the DEBUG constant
  t0001 (mingw): do not expect a specific order of stdout/stderr
  Mark .bat files as requiring CR/LF endings
  mingw: fix a typo in the msysGit-specific section