add documentation for block/unblock control commands
add tag command to the refcard
<p>For <a href="Developer.html#tags">their meanings</a> please consult the
general developers' documentation for the $gBug system.
+<dt><code>block</code>|<code>unblock</code> <var>bugnumber</var> <code>by</code>|<code>with</code> <var>bug</var> [ <var>bug</var> ... ]
+
+ <dd>Use to note that one bug blocks another bug from being fixed.
+ The first listed bug is the one being blocked, and it is followed
+ by the bug or bugs that are blocking it. Use <code>unblock</code>
+ to unblock a bug.
+
+ <p>Example usage:</p>
+
+ <pre>
+ # indicates that 7890 cannot be fixed until 123456 is fixed
+ block 7890 by 123456
+ # indicates that 7890 can be fixed before 123456 after all
+ unblock 7890 by 123456
+ </pre>
+
<dt><code>close</code> <var>bugnumber</var> [ <var>fixed-version</var> ]
(deprecated)
<li><code>retitle</code> <var>bugnumber</var> <var>new-title</var>
<li><code>merge</code> <var>bugnumber</var> <var>bugnumber</var> ...
<li><code>unmerge</code> <var>bugnumber</var>
+ <li><code>tag</code> <var>bugnumber</var> [+-=] <var>tag</var> ...
+ <li><code>block</code> <var>bugnumber</var> <code>by</code> <var>bug</code> ...
+ <li><code>unblock</code> <var>bugnumber</var> <code>by</code> <var>bug</code> ...
</ul>
<p><code>reopen</code> with <code>=</code> or no originator address leaves