Add the rebase.exe tool to be able to fix msys-1.0.dll
Depending on your setup, the base address of msys-1.0.dll might clash
with other .dll files' addresses. The symptom looks like this:
assertion "!inheap (s)" failed: file "../../../../src/winsup/cygwin/cygheap.cc", line 309
In such a case, simply fire up cmd.exe, change the working directory to
$MSYSGIT_ROOT/bin and execute something like
..\mingw\bin\rebase -b 0x67000000 msys-1.0.dll
The rebase.exe tool was cherry-picked from the 'full' branch, where it
was built from /src/rebase/.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>