Port callgrind_control to vgdb

Port callgrind_control to vgdb

Same functionality, apart from "-l" to show "long information".
This only printed the current working directory of the callgrind run,
which currently is not available any longer, but not really needed.

The port to vgdb has an important benefit:
callgrind can now be controlled by callgrind_control also when
the client program is blocked/sleeping in a system call. This was
not possible before as a command file was polled only while the
client was running.

Ubuntu by default restricts PTRACE (used by vgdb) to parent processes,
making Ubuntu show similar behavior as before: vgdb is not allowed
to attach by PTRACE when the client is blocked/sleeping, so
callgrind_control works similar to before this change on Ubuntu.

A final patch, which gets rid of command file polling, will be
submitted after Valgrind 3.7, as KCachegrind currently writes
command files directly, and needs to be changed to rely on
callgrind_control instead.

git-svn-id: svn://svn.valgrind.org/valgrind/trunk@11867