sqlite3: Enabling option to disable filesystem locking (POSIX advisory locks)

When sqlite database is expected to be stored on a NFS disk (e.g., a
home directory and ~/.ndnx/ndnsec-public-info.db is on NFS mount),
default POSIX advisory filesystem locks may not work properly, since
some NFS implementation do not support them.  This commit allows
specification of ``--without-sqlite-locking`` to use alternative
"dotfile" sqlite locking mechanism.

Change-Id: Iddee82c6ca7839f993147547f61c440184689043
build: Experimental support to build using precompiled headers

This type of build needs to be explicitly enabled using --with-pch
configure option.

Change-Id: I02dc304187d54c3cf40f1d51b1b11b21f868e225