Add a '$' in the __git_ps1 output to show stashed changes are present,
when GIT_PS1_SHOWSTASHSTATE is set to a nonempty value.
The code for checking if the stash has entries is taken from
'git-stash.sh'.
Signed-off-by: Daniel Trstenjak <daniel.trstenjak@online.de> Acked-by: Shawn O. Pearce <spearce@spearce.org> Signed-off-by: Junio C Hamano <gitster@pobox.com>