Makefile: add PYTHON_PATH to GIT-BUILD-OPTIONS

The PYTHON_PATH environment variable is not set when running test scripts
manually i.e. when not using 'make test'.  Scripts which attempt to use
this variable will fail.  So add it to the list of variables written to
the GIT-BUILD-OPTIONS file so that the test suite will import it when
running the test scripts.

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -1885,6 +1885,7 @@ GIT-CFLAGS: FORCE
 GIT-BUILD-OPTIONS: FORCE
 	@echo SHELL_PATH=\''$(subst ','\'',$(SHELL_PATH_SQ))'\' >$@
 	@echo PERL_PATH=\''$(subst ','\'',$(PERL_PATH_SQ))'\' >>$@
+	@echo PYTHON_PATH=\''$(subst ','\'',$(PYTHON_PATH_SQ))'\' >>$@
 	@echo TAR=\''$(subst ','\'',$(subst ','\'',$(TAR)))'\' >>$@
 	@echo NO_CURL=\''$(subst ','\'',$(subst ','\'',$(NO_CURL)))'\' >>$@
 	@echo NO_PERL=\''$(subst ','\'',$(subst ','\'',$(NO_PERL)))'\' >>$@