BUG/TST: Allow generators in DataFrame.from_record.

- nrows implementation doesn't allow unknown size iterator like
generators, if nrows = none ends with a TypeError.
- To allow generators if nrows=None consume it into a list.
- Add two tests of generators input.
- Add release notes for #4910
Merge branch 'master' of https://github.com/tinproject/pandas into tinproject-master

Conflicts:
	doc/source/release.rst