moodlelib: moodle_request_shutdown() prints included files

moodlelib: moodle_request_shutdown() prints included files

If MDL_PERFINC is defined, we now print to errorlog a listing
of the files included, their size, and then a total size.

The total size isn't the most important metric, though it does give us
a good idea of how much PHP the PHP engine is parsing for us. The main
cost is still in the seeks involved.

Even when using precompilers -- our best-case scenario -- each include
or require forces at least 2 stat()s to compare timestamps in the php
file vs the precompiled file. If the working set fits in buffers we are
fine, but our 60+ stat() calls per page is quite a bit.