fix --enable-laldetchar option help

laldetchar support is enabled by default, reflect this in the help
message for the option
enable lalxml support by default

originally this was disabled by default as it linked against libxml2
which in turn was linked against the pthread library. as such this
caused problems as condor_compile could then not be used. however on the
current reference platorms libxml2 is not linked against pthreads.