ui-diff: Add link to ignore/show whitespace changes in diffs

Add a link to the "Diffstat" line to ignore/show whitespace changes in the
generated diff.

To support this, cgit_commit_link() and cgit_diff_link() has learned to
preserve the ctx.qry.ignorews variable.

Signed-off-by: Johan Herland <johan@herland.net>

ui-shared.c

@@ -349,6 +349,11 @@ void cgit_commit_link(char *name, const char *title, const char *class,
 		htmlf("%d", ctx.qry.context);
 		delim = "&";
 	}
+	if (ctx.qry.ignorews) {
+		html(delim);
+		html("ignorews=1");
+		delim = "&";
+	}
 	html("'>");
 	html_txt(name);
 	html("</a>");
@@ -397,6 +402,11 @@ void cgit_diff_link(const char *name, const char *title, const char *class,
 		htmlf("%d", ctx.qry.context);
 		delim = "&amp;";
 	}
+	if (ctx.qry.ignorews) {
+		html(delim);
+		html("ignorews=1");
+		delim = "&amp;";
+	}
 	html("'>");
 	html_txt(name);
 	html("</a>");