Merge branch 'munmap-before-ext-diff'

This topic branch fixes the usage pattern where files are still held
open with an exclusive lock when an external program is asked to open
those very same files.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

diff.c

@@ -4190,6 +4190,10 @@ static void run_external_diff(const char *pgm,
 	argv_array_pushf(&env, "GIT_DIFF_PATH_COUNTER=%d", ++o->diff_path_counter);
 	argv_array_pushf(&env, "GIT_DIFF_PATH_TOTAL=%d", q->nr);
 
+	if (one && one->should_munmap)
+		diff_free_filespec_data(one);
+	if (two && two->should_munmap)
+		diff_free_filespec_data(two);
 	if (run_command_v_opt_cd_env(argv.argv, RUN_USING_SHELL, NULL, env.argv))
 		die(_("external diff died, stopping at %s"), name);