Added regression test for #1340.

Child process must produce > 4096 bytes on STDERR (e.g., a large PHP backtrace).
Fixed #1340: Reading from STDOUT or STDERR hangs forever on Windows if the output is too large.

See https://bugs.php.net/bug.php?id=51800
Ignore irrelevant test result differences.
Ignore irrelevant test result differences on HHVM.
Fixed XML::load() does not report libxml errors on Windows.
Fixed XML::load() fails to load relative XInclude paths on Windows.
Exclude system temp directory in stack traces on Windows.

PHPUnit_Util_PHP_Windows writes the process isolation script template into the Windows TEMP directory and loads the script by including the file, which causes an extraneous last stack frame in all test results on Windows.
Fixed PHPT file path expectations fail on Windows.
Include process isolation file prefix to avoid false-positive matches.
Merge pull request #1354 from sun/win-fail

PHPUnit test suite fails on Windows
Merge pull request #1345 from sun/runner-isolation-stderr-fatal-41

Process isolation blocks infinitely upon fatal error in child process
Allow a test to identify whether it runs in isolation.

A custom setup of test fixtures may use this indicator to skip additional performance optimizations that only make sense if multiple tests are executed in the same process.
Fixed segmentation fault on PHP 5.3.3 caused by test fixtures.
Split value from assertion.
Use !empty().
Renamed to isInIsolation().