Add redzone and statistics reporting to debug allocator.

Add redzone and statistics reporting to debug allocator.

src/alloc-srvx.c (redzone): New variable to detect buffer overwrites.
(alloc_count, alloc_size): New variables to track allocation stats.
(srvx_malloc, srvx_realloc, srvx_free): Use the above.

src/opserv.c (OSMSG_STATS_MEMORY): New translation string.
(cmd_stats_memory): New (conditional) command function.
(init_opserv): Conditionally provide cmd_stats_memory.
git-archimport-id: srvx@srvx.net--2005-srvx/srvx--devo--1.3--patch-5