Add slab allocator; reduce delta with srvx-gs.

Add slab allocator; reduce delta with srvx-gs.

configure.in: Check for getpagesize().  Support --with-malloc=slab.

src/Makefile.am: Add alloc-slab.c as an extra source file.

src/alloc-srvx.c: Clean up srvx_free() slightly.  Check for previously
allocated blocks.

srvx.conf.example, src/chanserv.c, src/main.c, src/modcmd.c,
src/proto-p10.c: Apply patches to bring closer to srvx-gs branch.

src/log.c: Assert and _exit() on fatal log messages.

src/opserv.c: Clarify logic for modes to set on join floods.

src/proto-common.c: Accept off-channel commands in registered channels.
git-archimport-id: srvx@srvx.net--2005-srvx/srvx--devo--1.3--patch-10