userdiff: add xdiff_clear_find_func()

xdiff_set_find_func() is used to set user defined regular expressions
for finding function signatures.  Add xdiff_clear_find_func(), which
frees the memory allocated by the former, making the API complete.

Also, use the new function in diff.c (the only call site of
xdiff_set_find_func()) to clean up after ourselves.
Signed-off-by: NRene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

diff.c

@@ -1603,6 +1603,7 @@ static void builtin_diff(const char *name_a,
 			free(mf1.ptr);
 		if (textconv_two)
 			free(mf2.ptr);
+		xdiff_clear_find_func(&xecfg);
 	}
 
  free_ab_and_return:

xdiff-interface.c

@@ -309,6 +309,21 @@ void xdiff_set_find_func(xdemitconf_t *xecfg, const char *value, int cflags)
 	}
 }
 
+void xdiff_clear_find_func(xdemitconf_t *xecfg)
+{
+	if (xecfg->find_func) {
+		int i;
+		struct ff_regs *regs = xecfg->find_func_priv;
+
+		for (i = 0; i < regs->nr; i++)
+			regfree(&regs->array[i].re);
+		free(regs->array);
+		free(regs);
+		xecfg->find_func = NULL;
+		xecfg->find_func_priv = NULL;
+	}
+}
+
 int git_xmerge_style = -1;
 
 int git_xmerge_config(const char *var, const char *value, void *cb)

xdiff-interface.h

@@ -21,6 +21,7 @@ int read_mmfile(mmfile_t *ptr, const char *filename);
 int buffer_is_binary(const char *ptr, unsigned long size);
 
 extern void xdiff_set_find_func(xdemitconf_t *xecfg, const char *line, int cflags);
+extern void xdiff_clear_find_func(xdemitconf_t *xecfg);
 extern int git_xmerge_config(const char *var, const char *value, void *cb);
 extern int git_xmerge_style;