hgweb: add z-index for search field tooltip

hgweb: add z-index for search field tooltip

On graph page, search field tooltip sometimes goes down to the graph area,
where it used to be covered by foreground element of graph entries (.fg)
because they have z-index: 10.

To prevent the tooltip from being covered, z-index: 15 is enough.

--- a/mercurial/templates/static/style-gitweb.css	Wed Jun 27 07:19:30 2018 -0700
+++ b/mercurial/templates/static/style-gitweb.css	Thu Jun 28 07:41:08 2018 +0800
@@ -74,6 +74,7 @@
   background: #ffc;
   border: 1px solid yellow;
   border-radius: 5px;
+  z-index: 15;
 }
 
 #searchform:hover div#hint { display: block; }

--- a/mercurial/templates/static/style-paper.css	Wed Jun 27 07:19:30 2018 -0700
+++ b/mercurial/templates/static/style-paper.css	Thu Jun 28 07:41:08 2018 +0800
@@ -90,6 +90,7 @@
   font-size: 70%;
   border: 1px solid yellow;
   border-radius: 5px;
+  z-index: 15;
 }
 
 form.search:hover div#hint { display: block; }

--- a/tests/test-hgweb.t	Wed Jun 27 07:19:30 2018 -0700
+++ b/tests/test-hgweb.t	Thu Jun 28 07:41:08 2018 +0800
@@ -336,7 +336,7 @@
 
   $ get-with-headers.py --twice localhost:$HGPORT 'static/style-gitweb.css' - date etag server
   200 Script output follows
-  content-length: 9059
+  content-length: 9074
   content-type: text/css
   
   body { font-family: sans-serif; font-size: 12px; border:solid #d9d8d1; border-width:1px; margin:10px; background: white; color: black; }
@@ -415,6 +415,7 @@
     background: #ffc;
     border: 1px solid yellow;
     border-radius: 5px;
+    z-index: 15;
   }
   
   #searchform:hover div#hint { display: block; }