Allow CFLGAS="-std=c99 -D_POSIX_C_SOURCE=2"

Use glib function:
strcasecmp -> g_ascii_strcasecmp
bzero -> memset
strdup -> g_strdump

Don't use arithmetic void*+int
Decrease POSIX required level to 1

One can now compile with CFLAGS="-std=c99 -D_POSIX_C_SOURCE=1 -pedantic"

Trade getopt.h function for glib equivalents:
This mean all utilities now have long option names.
Adjust manuals and bash_completion accordingly.

Added missing manual and bash_completion for mdb-import.
Avoid dynamic array allocation on stack.

This might help some non C99 compliant compilers, while being a trivial change.