Do not convert series when looking at sub-daily frequencies.
Merge branch 'infer_freq' of https://github.com/rockg/pandas into rockg-infer_freq

Conflicts:
	doc/source/whatsnew/v0.15.2.txt
Fix unrecognized 'Z' UTC designator
Merge branch 'fix-z-designator' of https://github.com/broessli/pandas into broessli-fix-z-designator

Conflicts:
	doc/source/whatsnew/v0.15.2.txt
Revert "Fix unrecognized 'Z' UTC designator"

This reverts commit 0e02d5f275234b11d699ce13aa4da4f3624d0f7d.

Conflicts:
	doc/source/whatsnew/v0.15.2.txt
BUG CSV: fix problem with trailing whitespace, issues 8661, 8679
ENH CSV: improve memory footprint when skipping first N rows, issue 8681