Add possibility to switch between unidiff and side-by-side-diff.

A new config option side-by-side-diffs added, defaulting to 0,
meaning unidiff. Also a query option (ss) is used toggle this.

In the commit page you can switch between the two diff formats by
clicking on the link on the "commit"-row, to the right of (patch).

In the diff page you can switch by using the link at the start
of the page.

All commit-links and diff-links will remember the choice.

Signed-off-by: Ragnar Ouchterlony <ragnar@lysator.liu.se>
Signed-off-by: Lars Hjemli <hjemli@gmail.com>

cgit.c

@@ -182,6 +182,8 @@ void config_cb(const char *name, const char *value)
 		ctx.cfg.summary_branches = atoi(value);
 	else if (!strcmp(name, "summary-tags"))
 		ctx.cfg.summary_tags = atoi(value);
+	else if (!strcmp(name, "side-by-side-diffs"))
+		ctx.cfg.ssdiff = atoi(value);
 	else if (!strcmp(name, "agefile"))
 		ctx.cfg.agefile = xstrdup(value);
 	else if (!strcmp(name, "renamelimit"))
@@ -238,6 +240,8 @@ static void querystring_cb(const char *name, const char *value)
 		ctx.qry.showmsg = atoi(value);
 	} else if (!strcmp(name, "period")) {
 		ctx.qry.period = xstrdup(value);
+	} else if (!strcmp(name, "ss")) {
+		ctx.qry.ssdiff = atoi(value);
 	}
 }
 
@@ -279,6 +283,7 @@ static void prepare_context(struct cgit_context *ctx)
 	ctx->cfg.summary_branches = 10;
 	ctx->cfg.summary_log = 10;
 	ctx->cfg.summary_tags = 10;
+	ctx->cfg.ssdiff = 0;
 	ctx->env.cgit_config = xstrdupn(getenv("CGIT_CONFIG"));
 	ctx->env.http_host = xstrdupn(getenv("HTTP_HOST"));
 	ctx->env.https = xstrdupn(getenv("HTTPS"));