gitweb: provide a way to customize html headers

This allows web sites to add some specific html headers to the pages
generated by gitweb.

The new variable $site_html_head_string can be set to an html snippet that
will be inserted at the end of the <head> section of each page generated
by gitweb.

Signed-off-by: Lénaïc Huard <lenaic@lhuard.fr.eu.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/gitweb/INSTALL b/gitweb/INSTALL
index d134ffe..6d45406 100644
--- a/gitweb/INSTALL
+++ b/gitweb/INSTALL
@@ -130,6 +130,8 @@
    Points to an .html file which is included on the gitweb project
    overview page ('projects_list' view), if it exists.  Relative to
    gitweb.cgi script.  [Default: indextext.html]
+ * GITWEB_SITE_HTML_HEAD_STRING
+   html snippet to include in the <head> section of each page. [No default]
  * GITWEB_SITE_HEADER
    Filename of html text to include at top of each page.  Relative to
    gitweb.cgi script.  [No default]
diff --git a/gitweb/Makefile b/gitweb/Makefile
index 1c85b5f..e65fc27 100644
--- a/gitweb/Makefile
+++ b/gitweb/Makefile
@@ -34,6 +34,7 @@
 GITWEB_LOGO = static/git-logo.png
 GITWEB_FAVICON = static/git-favicon.png
 GITWEB_JS = static/gitweb.js
+GITWEB_SITE_HTML_HEAD_STRING =
 GITWEB_SITE_HEADER =
 GITWEB_SITE_FOOTER =
 HIGHLIGHT_BIN = highlight
@@ -144,6 +145,7 @@
 	-e 's|++GITWEB_LOGO++|$(GITWEB_LOGO)|g' \
 	-e 's|++GITWEB_FAVICON++|$(GITWEB_FAVICON)|g' \
 	-e 's|++GITWEB_JS++|$(GITWEB_JS)|g' \
+	-e 's|++GITWEB_SITE_HTML_HEAD_STRING++|$(GITWEB_SITE_HTML_HEAD_STRING)|g' \
 	-e 's|++GITWEB_SITE_HEADER++|$(GITWEB_SITE_HEADER)|g' \
 	-e 's|++GITWEB_SITE_FOOTER++|$(GITWEB_SITE_FOOTER)|g' \
 	-e 's|++HIGHLIGHT_BIN++|$(HIGHLIGHT_BIN)|g'
diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 70a576a..d335108 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -85,6 +85,8 @@
 our $site_name = "++GITWEB_SITENAME++"
                  || ($ENV{'SERVER_NAME'} || "Untitled") . " Git";
 
+# html snippet to include in the <head> section of each page
+our $site_html_head_string = "++GITWEB_SITE_HTML_HEAD_STRING++";
 # filename of html text to include at top of each page
 our $site_header = "++GITWEB_SITE_HEADER++";
 # html text to include at home page
@@ -3868,6 +3870,11 @@
 		print "<base href=\"".esc_url($base_url)."\" />\n";
 	}
 	print_header_links($status);
+
+	if (defined $site_html_head_string) {
+		print to_utf8($site_html_head_string);
+	}
+
 	print "</head>\n" .
 	      "<body>\n";