mlockall() -> mlock()

mlockall() -> mlock()

This patch adds a new implementation of locking function instead
of mlockall() that may lock way too much memory (>100MB).
New function instead uses mlock() system call and selectively locks
memory areas from /proc/self/maps trying to avoid locking areas
unused during lock-ed state.

Patch also adds struct cmd_context to all memlock() calls to have
access to configuration.

For backward compatibility functionality of mlockall()
is preserved with "activation/use_mlockall" flag.

As a simple check, locking and unlocking counts the amount of memory
and compares whether values are matching.