Replace code for finding ControlProtocols/Surface plugins with a portable equivalent.

Replace code for finding ControlProtocols/Surface plugins with a portable equivalent.

Remove Session::control_protocol_path and the supporting non-portable
Session::suffixed_search_path from Session.

Add ARDOUR::control_protocol_search_path which is used in place of
Session::control_protocol_path

Replace ARDOUR::get_system_module_path with ARDOUR::system_module_directory which
is used by ARDOUR::control_protocol_search_path

Export ARDOUR_SURFACES_PATH in gtk2_ardour/ardev_common.sh which is returned
by ARDOUR::control_protocol_search_path if defined. This means the control surfaces
in the libs/surfaces/* directories can now be used without installing them.

Add pbd/file_utils.h/cc containing functions for finding files matching a certain
pattern

Update documentation in SearchPath and add another constructor that takes
a sys::path

git-svn-id: svn://localhost/ardour2/trunk@2049 d708f5d6-7413-0410-9779-e7cbd77b26cf