Merge remote-tracking branch 'breznak/modular-numpy' into python27

Conflicts:
	external/common/requirements.txt
Incorporating feedback from scott and others in order to get this branch approved.

Conflicts:
	build.sh
Triple verbosity and removing --target in favor of --prefix in --install-option
Removed popd from cleanUpEnv causing builds to fail.
Removing the now-redundant --install-scripts install option
Removing the --ignore-installed CLI option.  When present, numpy will always
re-compile/re-install which is not the desired behavior and by not specifying
it on the command line, the user can always override with either a pip config
file in $HOME, or by PIP_IGNORE_INSTALLED env variable.

Ultimately, we'll be getting rid of --find-links, --no-index, and --index-url
options too, so it makes sense to keep the pip command as light as possible.
Do a clean build in travis, set PIP_IGNORE_INSTALLED in cleanbuild.sh
Explicitly set PIP_IGNORE_INSTALLED in .travis.yml
Merge remote-tracking branch 'upstream/master' into python27
use python2,

in case of running in env where python3 is default, specify python2-config (both 2.6, 2.7 are OK)

Conflicts:
	build_system/unix/configure.ac
avoid repeting paths in $PATH when running env.sh multiple times

otherwise, new paths are concateted to the old ones

Conflicts:
	env.sh
document choice of TP implementation

TP10X2 is fast,optimized implementation using C++ code
TP is python, simple, slow

Conflicts:
	examples/tp/hello_tp.py
add python2-config to Linux platform

to ntaplatform_python_libs to keep consistency with Mac
Support multiple versions
Use stringify and expand_and_stringify technique from http://stackoverflow.com/a/9096509/1781435