html: improve parsing of tables

When foster parenting, merge adjacent text nodes.
Properly close table row at </tr> tag.

Pass tests1.dat, test 32:
<!-----><font><div>hello<table>excite!<b>me!<th><i>please!</tr><!--X-->

| <!-- - -->
| <html>
|   <head>
|   <body>
|     <font>
|       <div>
|         "helloexcite!"
|         <b>
|           "me!"
|         <table>
|           <tbody>
|             <tr>
|               <th>
|                 <i>
|                   "please!"
|             <!-- X -->

R=nigeltao
CC=golang-dev
https://golang.org/cl/5323048
2 files changed