lalsuite_build.m4: remove any /opt/... and /usr/... path elements when using LALSUITE_ADD_PATH
XLALError.h: exclude most functions and macros from SWIG interface

- Only XLALErrorValue enum and XLALSetErrno(), etc. functions are exposed
- Prevents XLAL error macros from being expanded within SWIG-related code
Revert "Remove SWIG from build dependencies of LALSuite Debian/RPM packages"

This reverts commit b70c381d85766496148003df9ce263500d2c57b5.
SWIG: remove bundling of generated sources in distribution tarballs

- does not work well enough with LALSuite packaging
- sundry other minor changes to SWIG bindings