CCBC-403: Restore 'compat' memcached functionality

This provides proper memcached support. In addition to the previous
commits which add necessary prerequisites, this commit:

- Adds a new scheme, memcached://
- A new configuration provider (LCB_CLCONFIG_MCRAW)
- defines the LCB_CONFIG_MCCOMPAT_PORT for the default 11211 memcached
  port
- Before switching to HTTP streaming config, check that the current
  configuration is not a raw memcached config.

Tested with memcached 1.4.13

Change-Id: I0372ac802718a75d9d70de92c5a6eb16ad641f20
Reviewed-on: http://review.couchbase.org/38752
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Brett Lawson <brett19@gmail.com>