Cygwin expects forward slashes for commands to be run via sh.exe

Cygwin expects forward slashes for commands to be run via sh.exe

FS_Win32_Cygwin replaces backslashes by / as a side-effect of
relativize(). When support for core.hooksPath was added, paths were
relativized in a different place using Path.resolve(), which doesn't
do that transformation. As a result hooks could not be run on Cygwin
in some cases.

Do the transformation in FS_Win32_Cygwin.runInShell(). In all other
places, File or Path objects are used, which give no guarantee about
the file separator (typically the system-dependent default separator),
so doing the transformation earlier still wouldn't guarantee that
sh.exe indeed gets a command string using forward slashes.

Bug: 558577
Change-Id: I3c07eb85f0ac7c5628a2e92f990e5cdb7ecf532f
Signed-off-by: Thomas Wolf <thomas.wolf@paranor.ch>