new tests for EXPIRE family functions, new millisecond precision, and new millisecond argument variants.

Initial implementation of a client-server parallel testing system for Redis in order to speedup execution of the test suite.

fixed bgsave_in_progress in INFO when BGSAVEing with diskstore enabled, don't DEBUG FLUSHCACHE when bgsave is in progress.

SUBSTR is renamed to GETRANGE to have better consistency between command
names (with SETRANGE as its dual). GETRANGE is still aliased as SUBSTR.

changed how server.tcl accepts options to support more directives without requiring more arguments to the proc