Fix error_get_last() not cleared when error handle function entered

Summary: This also :
  - make get_last_error() not available in error handler like
    PHP, see http://3v4l.org/QKQKY
  - clear last error when request shutdown, prevent errmessage
    leak to the next request

Closes #4407
Closes https://github.com/facebook/hhvm/pull/4414

Reviewed By: @JoelMarcey

Differential Revision: D1727912

Signature: t1:1727912:1418338155:ce9f5e5568231a18c6b45ff6247cf2182471e5eb
Mock date/time functions in Isolation.php

Summary: Mock date/time functions (e.g. time() ) so they never return the same value when calling multiple times.
By doing so, more flakey test cases can be found.

Closes https://github.com/facebook/hhvm/pull/4384

Reviewed By: @JoelMarcey

Differential Revision: D1719095

Signature: t1:1719095:1418338273:e3867d429e3162f1110e96b1c16677da5872d8c0
Disable PGO for pseudo-mains

Summary: JITing pseudo-mains requires extra checks that blow the IR.  PGO can
significantly increase the size of the regions, so disable it for
pseudo-mains (so regions will be just tracelets).

Reviewed By: @swtaarrs

Differential Revision: D1734379
Add PHP_INT_MIN

Summary: `PHP_INT_MIN` constant was added in php-src (https://github.com/php/php-src/pull/755)

Let's add it too.

Had to go through some IDL to code generation hoops because of possible overflow issues
with min int64_t with the `-` unary operator.

Reviewed By: @markw65

Differential Revision: D1724355

Signature: t1:1724355:1418051922:434367e548de2539916b55b3b3510294a2bfe608