Lowered shared memory event buffer size
Lowered shared memory event buffer size

Profiling showed the old event buffer size (2^20 events)
was dominating the cache and causing lots of icache misses.

Dropped the size to 2^12 events to get more scalable
performance with more threads

mikelui/Sigil2,mikelui/Sigil2,VANDAL/sigil2,mdlui/Sigil2,mdlui/Sigil2,mikelui/Sigil2,mdlui/Sigil2,VANDAL/sigil2,mikelui/Sigil2,VANDAL/sigil2,mdlui/Sigil2