Set focus on proofing interface S/R Search field

When the Search/Replace tool is popped in the proofing interface,
ensure the keyboard focus is in its Search field. This enables
the proofer to begin typing the Search term immediately without
an additional click.

tools/proofers/srchrep.php

@@ -17,7 +17,7 @@
 <tr><td class="right-align">
 <?php echo _("Search"); ?>:
 </td><td>
-<input type="text" name="search" id='search'>
+<input type="text" name="search" id='search' autofocus>
 </td></tr>
 <tr><td class="right-align">
 <?php echo _("Replace"); ?>: