diff: rename 'this' variables

Rename C++ keyword in order to bring the codebase closer to being able
to be compiled with a C++ compiler.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/diff.c b/diff.c
index 0a9a0cd..f7df227 100644
--- a/diff.c
+++ b/diff.c
@@ -2594,14 +2594,14 @@ struct dirstat_dir {
 static long gather_dirstat(struct diff_options *opt, struct dirstat_dir *dir,
 		unsigned long changed, const char *base, int baselen)
 {
-	unsigned long this_dir = 0;
+	unsigned long sum_changes = 0;
 	unsigned int sources = 0;
 	const char *line_prefix = diff_line_prefix(opt);
 
 	while (dir->nr) {
 		struct dirstat_file *f = dir->files;
 		int namelen = strlen(f->name);
-		unsigned long this;
+		unsigned long changes;
 		char *slash;
 
 		if (namelen < baselen)
@@ -2611,15 +2611,15 @@ static long gather_dirstat(struct diff_options *opt, struct dirstat_dir *dir,
 		slash = strchr(f->name + baselen, '/');
 		if (slash) {
 			int newbaselen = slash + 1 - f->name;
-			this = gather_dirstat(opt, dir, changed, f->name, newbaselen);
+			changes = gather_dirstat(opt, dir, changed, f->name, newbaselen);
 			sources++;
 		} else {
-			this = f->changed;
+			changes = f->changed;
 			dir->files++;
 			dir->nr--;
 			sources += 2;
 		}
-		this_dir += this;
+		sum_changes += changes;
 	}
 
 	/*
@@ -2629,8 +2629,8 @@ static long gather_dirstat(struct diff_options *opt, struct dirstat_dir *dir,
 	 *    under this directory (sources == 1).
 	 */
 	if (baselen && sources != 1) {
-		if (this_dir) {
-			int permille = this_dir * 1000 / changed;
+		if (sum_changes) {
+			int permille = sum_changes * 1000 / changed;
 			if (permille >= dir->permille) {
 				fprintf(opt->file, "%s%4d.%01d%% %.*s\n", line_prefix,
 					permille / 10, permille % 10, baselen, base);
@@ -2639,7 +2639,7 @@ static long gather_dirstat(struct diff_options *opt, struct dirstat_dir *dir,
 			}
 		}
 	}
-	return this_dir;
+	return sum_changes;
 }
 
 static int dirstat_compare(const void *_a, const void *_b)