Jemalloc-support: Added --with-jemalloc configure option

Selecting jemalloc, prevents static linking of rocksdb, as it
is dependent on tcmalloc. Default option remains tcmalloc.
Package build builds with tcmalloc support. Support for 
jemalloc in package build and perf stats/heap profiler is 
underway.

Signed-off-by: shishir gowda <shishir.gowda@sandisk.com>
My concern is that if you do --with-librocksdb-static --with-jemalloc you will get jemalloc but no rocksdb.  If that is not a valid combination it should throw an error.