Added possibility to add extra variables for a given external
Add possibility to create extra env variable for a given external. An extra list of pairs can be added to the one defining which external to add and what to add to the path. If that list is present, an _HOME env var will be set which will be useable in the following vatiable definitions like so:
[
"pytools",
"1.9_python2.7",
[
"bin",
"python"
],
[
["PYTOOLS_TEST", "${PYTOOLS_HOME}/test"]
]
]