Revert "Update libsqlite3"

This reverts commit e7bc03023a1b0311cabdb4272894453cc188e866.

Closes #4
Install headers

Must be applied after the associated hhvm commit "Don't require full
source tree for building DSOs".
fix compilation with Centos 5.8

LifoSem and MemoryIdler use detail/Futex.h (Futex had been disabled already) that don't compile at Centos 5.8 - Linux 2.6.18 , because FUTEX_WAIT_BITSET, FUTEX_WAKE_BITSET, FUTEX_CLOCK_REALTIME aren't defined
fix compilation with Centos 5.8

wangle/ThreadGate depends at folly/detail/Futex.h and isn't used in hhvm
Defer evaluation of CMAKE_INSTALL_PREFIX

Per #2765. This change should not be needed to close the bug, but it's
probably a good idea.
add fastlz library for ext_memcached

The PHP memcached extension (which ext_memcached emulates) uses fastlz
compression by default. A follow-up commit to hhvm/hhvm will add fastlz support
for the HHVM extension.
add a pthread time lock shim
add system-agnostic time functions
implement __GNUC_PREREQ/__GLIBC_PREREQ on systems that don't have it