Use is_absolute_path() in diff-lib.c, lockfile.c, setup.c, trace.c

Using the helper function to test for absolute paths makes porting easier.

Signed-off-by: Steffen Prohaska <prohaska@zib.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff-lib.c

@@ -231,7 +231,7 @@ static int handle_diff_files_args(struct rev_info *revs,
 static int is_outside_repo(const char *path, int nongit, const char *prefix)
 {
 	int i;
-	if (nongit || !strcmp(path, "-") || path[0] == '/')
+	if (nongit || !strcmp(path, "-") || is_absolute_path(path))
 		return 1;
 	if (prefixcmp(path, "../"))
 		return 0;

lockfile.c

@@ -94,7 +94,7 @@ static char *resolve_symlink(char *p, size_t s)
 			return p;
 		}
 
-		if (link[0] == '/') {
+		if (is_absolute_path(link)) {
 			/* absolute path simply replaces p */
 			if (link_len < s)
 				strcpy(p, link);

setup.c

@@ -59,7 +59,7 @@ const char *prefix_path(const char *prefix, int len, const char *path)
 const char *prefix_filename(const char *pfx, int pfx_len, const char *arg)
 {
 	static char path[PATH_MAX];
-	if (!pfx || !*pfx || arg[0] == '/')
+	if (!pfx || !*pfx || is_absolute_path(arg))
 		return arg;
 	memcpy(path, pfx, pfx_len);
 	strcpy(path + pfx_len, arg);

trace.c

@@ -37,7 +37,7 @@ static int get_trace_fd(int *need_close)
 		return STDERR_FILENO;
 	if (strlen(trace) == 1 && isdigit(*trace))
 		return atoi(trace);
-	if (*trace == '/') {
+	if (is_absolute_path(trace)) {
 		int fd = open(trace, O_WRONLY | O_APPEND | O_CREAT, 0666);
 		if (fd == -1) {
 			fprintf(stderr,