This patch adds convenience functions to work with absolute paths.
The function is_absolute_path() should help the efforts to integrate
the MinGW fork.
Note that make_absolute_path() returns a pointer to a static buffer.
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>