cache SuperVersion in thread local storage to avoid mutex lock

Summary: as title

Test Plan:
asan_check
will post results later

Reviewers: haobo, igor, dhruba, sdong

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16257
Refine the checks in InfoLogLevel test.

Summary:
InfoLogLevel test now checks the number of lines of the output log file
instead of the number of bytes in the log file.

This diff fixes the issue that the previous InfoLogLevel test in
auto_roll_logger_test passed in make check but fails when valgrind
is used.

Test Plan: run with make check and valgrind.

Reviewers: kailiu

Reviewed By: kailiu

CC: leveldb

Differential Revision: https://reviews.facebook.net/D16407
Fix the [-Werror=sign-compare] issues

Summary:

Test Plan:

Reviewers:

CC:

Task ID: #

Blame Rev:
Fix some compilation bugs in different platforms

Summary:

detect some problems when testing my 3rd party release tool.