Re-organize the way to produce stacktrace.

Re-organize the way to produce stacktrace.

Since we introduced the API to set signal handler and print a
stacktrace, we should avoid glibc's backtrace, which may call malloc.
Basically, we choose the way to produce a stacktrace as same as
perftools.

Also, I removed GetStackFrames, which is not used and not implemented
with glibc.

git-svn-id: https://google-glog.googlecode.com/svn/trunk@16 eb4d4688-79bd-11dd-afb4-1d65580434c0