path: add type checking for path inputs

This commit adds type checking of path inputs to exported methods
in the path module. The exception is _makeLong(), which seems to
explicitly support any data type.

Fixes: https://github.com/iojs/io.js/issues/1139
PR-URL: https://github.com/iojs/io.js/pull/1153


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Brendan Ashworth <brendan.ashworth@me.com>