Add new as-yet unused asyncronous gdb attaching code.  Gdb can take a while to attach to a process, expecially if it's got lots of shared librarys which need to be loaded off a shared filesystems, this change adds the option to asyncronously attach meaning that padb can launch a instance of gdb for every target process on a node, tell them all to attach and allow them to procede in parallel.  This should help the performance a lot, particuarly on nodes with lots of cores.
Add new as-yet unused asyncronous gdb attaching code.  Gdb can take a
while to attach to a process, expecially if it's got lots of shared
librarys which need to be loaded off a shared filesystems, this change
adds the option to asyncronously attach meaning that padb can launch
a instance of gdb for every target process on a node, tell them all to
attach and allow them to procede in parallel.  This should help the
performance a lot, particuarly on nodes with lots of cores.

ashleypittman/padb,ashleypittman/padb,ashleypittman/padb