[PATCH 0/7 v2] prefix discovery at runtime (on Windows)

This is the second version of the patch series that fixes discovery of the installation prefix at runtime on Windows. It introduces a compile flag RUNTIME_PREFIX, which can be set to explicitly request prefix computation at runtime.

You can find the first version at

  http://article.gmane.org/gmane.comp.version-control.git/92605

I mainly improved some of the commit messages and rebased to the current master.

PATCH 6/7 might need further discussion. Hannes noted that PATCH 6/7 touches a sensible part of exec_cmd.c, although he thinks that the proposed change might be good. See http://article.gmane.org/gmane.comp.version-control.git/92626 for his comment. I did not modify PATCH 6/7.

        Steffen

 [PATCH 1/7] Windows: Add workaround for MSYS' path conversion
 [PATCH 2/7] system_path(): Add prefix computation at runtime if RUNTIME_PREFIX set
 [PATCH 3/7] Refactor git_set_argv0_path() to git_extract_argv0_path()
 [PATCH 4/7] Glean libexec path from argv[0] for git-upload-pack and git-receive-pack.
 [PATCH 5/7] Add calls to git_extract_argv0_path() in programs that call git_config_*
 [PATCH 6/7] Modify setup_path() to only add git_exec_path() to PATH
 [PATCH 7/7] Windows: Revert to default paths and convert them by RUNTIME_PREFIX