[Tracker] Fix for issue with memory limits

[Ralph Böhme <rb netafp com>]

Hi

libtracker-common: memory limits on systems with large amounts of RAM

On systems with large amounts of RAM get_memory_total() could overflow
and return a negative value, as a result memory would be limited to
MEM_LIMIT_MIN (which is 256 MB atm).

diff:
<https://github.com/slowfranklin/tracker/commit/faf826c57ee33c9e29388c586f14b26451416934>

patch:
<https://github.com/slowfranklin/tracker/commit/faf826c57ee33c9e29388c586f14b26451416934.patch>

-Ralph