savedir: new symbol for fast-read version

* lib/savedir.h (SAVEDIR_SORT_FASTREAD): New symbol, for programs
like GNU cp that want to use SAVEDIR_SORT_INODE if available,
SAVEDIR_SORT_NONE otherwise.  Problem reported by Bernhard Voelker in:
http://lists.gnu.org/archive/html/coreutils/2014-02/msg00037.html
* NEWS: Recent changes are not that important.
parse-datetime: fix crash or infloop in TZ="" parsing

This was reported in http://bugs.gnu.org/16872
from the coreutils command: date -d 'TZ="""'

The infinite loop for this case was present since the
initial TZ="" parsing support in commit de95bdc2 29-10-2004.
This was changed to a crash or heap corruption depending
on the platform with commit 2e3e4195 18-01-2010.

* lib/parse-datetime.y (parse_datetime): Break out of the
TZ="" parsing loop once the second significant " is found.
Also skip over any subsequent whitespace to be consistent
with the non TZ= case.
* tests/test-parse-datetime.c: Add test cases for TZ="" parsing.