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>
Similarly, if you do --with-tcmalloc --with-jemalloc you will get jemalloc instead of an error. Better to get an error than a confusing result.  Can we leave this as a simple condition and add a new test that errors out if both are 1?  For now that means you need to do --without-tcmalloc --with-jemalloc, which is slightly annoying, but at least the result is unambiguous.

Also tcmalloc is the default right now but that may change in the future.
 
Thanks!