Fix refcounting opts for bc control flow

Summary: With bytecode control flow, refcounts won't necessarily match
at a merge point, but they should obey the conditions described in the
comment on Value::merge.

Reviewed By: @edwinsmith

Differential Revision: D1363640
Corrected strtok for when tokenizer fails at the end of the string

Summary: `strtok` did not consider tokenizer failures resuling from eof after trying to tokenize.

Fixes #2860

Reviewed By: @ptarjan

Differential Revision: D1367181
remove mtime and prefetch

Summary: A long long time ago, the hack server was using message passing to implement the shared heap.
Back then, it was faster to batch the messages. Because of that, we were keeping the set of
classes and functions used by a node in the previous run to prefetch them the next time.
All of this is completely useless today, since we use shared memory, batching is not helping
what so ever!

Reviewed By: @elgenie

Differential Revision: D1365410
make SimpleXML boolean casts even faster

Summary: This is a follow up to PR #2855.

When we need to build our element's child tree (sxe_get_prop_hash) to
determine if it casts to true/false, we can get away with bailing after
finding the first element.

In my small Magento siege tests these result in significant
improvements:

Before:
Transactions:               1551 hits
Transaction rate:           51.79 trans/sec
Lowest response time:       97ms
Callgrind:                  http://i.imgur.com/npxMo0q.png

After:
Transactions:               1730 hits
Transaction rate:           58.43 trans/sec
Lowest response time:       89ms
Callgrind:                  http://i.imgur.com/Dgojb9Y.png
Closes #2868

Reviewed By: @ptarjan

Differential Revision: D1368727

Pulled By: @JoelMarcey
Tolerate running this test from the hphp/ subdir

Summary: These ffile arguments were assuming the test was being run from outside
the hphp directory. This now tolerates both; any arguments that don't
exist are ignored.

Reviewed By: @swtaarrs

Differential Revision: D1369011