Summary:
Change namespace from leveldb to rocksdb. This allows a single
application to link in open-source leveldb code as well as
rocksdb code into the same process.

Test Plan: compile rocksdb

Reviewers: emayanke

Reviewed By: emayanke

CC: leveldb

Differential Revision: https://reviews.facebook.net/D13287

Summary: Some scripts (like regression_build_test.sh) redirect stdio to a tmp file and delete it on exit. This would miss the stack trace output on segfault. Output to stderr would hopefully show us the stack trace in the continuous build output.

Test Plan: ./signal_test, make check

Reviewers: dhruba

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D10485

Summary:
This diff provides the ability to print out a stacktrace when the process receives certain signals.
Currently, we enable this for the following signals (program error related):
SIGILL SIGSEGV SIGBUS SIGABRT
Application simply #include "util/stack_trace.h" and call leveldb::InstallStackTraceHandler() during initialization, if signal handler is needed. It's not done automatically when openning db, because it's the application(process)'s responsibility to install signal handler and some applications might already have their own (like fbcode).

Sample output:
Received signal 11 (Segmentation fault)
#0  0x408ff0 ./signal_test() [0x408ff0] /home/haobo/rocksdb/util/signal_test.cc:4
#1  0x40827d ./signal_test() [0x40827d] /home/haobo/rocksdb/util/signal_test.cc:24
#2  0x7f8bb183172e /usr/local/fbcode/gcc-4.7.1-glibc-2.14.1/lib/libc.so.6(__libc_start_main+0x10e) [0x7f8bb183172e] ??:0
#3  0x408ebc ./signal_test() [0x408ebc] /home/engshare/third-party/src/glibc/glibc-2.14.1/glibc-2.14.1/csu/../sysdeps/x86_64/elf/start.S:113
Segmentation fault (core dumped)

For each frame, we print the raw pointer, the symbol provided by backtrace_symbols (still not good enough), and the source file/line. Note that address translation is done by directly shell out to addr2line. ??:0 means addr2line fails to do the translation. Hacky, but I think it's good for now.

Test Plan: signal_test.cc

Reviewers: dhruba, MarkCallaghan

Reviewed By: dhruba

CC: leveldb

Differential Revision: https://reviews.facebook.net/D10173