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.

mercurial/templates/static/style-gitweb.css

@@ -74,6 +74,7 b' div#hint {'
   background: #ffc;
   border: 1px solid yellow;
   border-radius: 5px;
+  z-index: 15;
 }
 
 #searchform:hover div#hint { display: block; }

mercurial/templates/static/style-paper.css

@@ -90,6 +90,7 b' form.search div#hint {'
   font-size: 70%;
   border: 1px solid yellow;
   border-radius: 5px;
+  z-index: 15;
 }
 
 form.search:hover div#hint { display: block; }

tests/test-hgweb.t

@@ -336,7 +336,7 b' static file'
 
   $ 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 b' static file'
     background: #ffc;
     border: 1px solid yellow;
     border-radius: 5px;
+    z-index: 15;
   }
   
   #searchform:hover div#hint { display: block; }