Add support for explicitly dumping native stacks.

This change modifies debuggerd so that it can be used to grab
the native stacks of a process that has hung and not just crashed.
Note that only the root user can do this (for now).

adb shell debuggerd <tid>

Then use logcat to find the tombstone file that was generated
which will have the native stacks of all threads in the
requested process.  The specified thread will be shown first
and will also appear in the main log.

Also made some minor tweaks to libcorkscrew so that we
could handle statically compiled executables in the future
if we compiled the library statically.

Improved the "wait_for_user_action" function to support
volume down as an alternative for devices that do not
have home keys.

Removed a mess of gotos.

Change-Id: Ic149653986b0c2f503c7f0e8b7cb1f3be7c84d1e