When clearTimeouts was called on a timer multiple times, it would break the
doubly-linked list along with future timeouts. This patch fixes that.

This code is functionally equivalent, but in a simpler form.  Now new
parameters to `execFile` do not require `exec` to be refactored.

Originally added in commit 078a48a9, this code dealt with an optional
env parameter that was passed to `exec`.  The parameter was removed, but
this code was left.  As it serves no purpose, removing it.

makes validation of errors more flexible

fixes issue 464

Fixes issue 461

Fixes issue #457

Fixes new bug shown in test-http-allow-req-after-204-res.js pointed out by
Tom Carden <tom.carden@gmail.com>.

See note in test-securepair-client.js

See http://valgrind.org/docs/manual/mc-manual.html#mc-manual.rudefn

Rather than have the python literal string, use CMake's find_package
to find actual python executable. This is more useful if you have
both Python 2 and 3 installed. CMake currently only supports python 2
and so will automatically find that version

 * Removed useless include_directories
 * Print ssl library path in build summary
 * ExternalProject also exists on 2.8.0
 * include pummel tests when testing with ctest
 * Moved tests.cmake to test/CMakeList.txt
 * Removed inconsistent, unnecessary condition in else