Fixed issue #4902.

Extended _ensure_numeric to check if the value is a complex numbers.
Also it now tries to convert the value to a complex number if conversion to float fails.
Added PyDev project files to .gitignore.
Merge branch 'iss4902' of https://github.com/alefnula/pandas into alefnula-iss4902

Conflicts:
	doc/source/release.rst