Instrument the TPAC: add timelog() method to EGCatLoader

Instrument the TPAC: add timelog() method to EGCatLoader

Meant for timing how long events take to generate a single TPAC page,
the timelog() method will provide timing in microsecond granularity of
various events required to build the page.

To invoke: $self->timelog("Event description...");

Builds up a context variable named "timing" containing a list of
arrays; each array entry contains a time and the event description.

Disabled by default; to enable, set DEBUG_TIMING = 1 in
OpenILS/WWW/EGCatLoader.pm

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>