RASTLIB: add SDL video driver.
RASTLIB: add more resolutions.
INPUT: add SDL input driver.

Also make aspect optional.  You could achieve the same by setting
aspect_x = aspect_y = 0.
FILEIO: separate out wild list globber into fs_dos.c and fs_unix.c.

Also sluffed a boxf warning.
FILEIO: replace backslashes with DIR_DELIM and DIR_DELIM_STR.
FILEIO: add unix file io stubs.
PJ: add sdl initialisation procedure and link targets.
PJ: Runs! ... with a bunch of temp file hacks.

PJ Paint now runs in Linux!

You need to copy (or symlink) the resource directory into the current
directory, and make AA.MU lower-case.

Temp files are put into the current directory for now to get around
permissions and differences between Unix and Windows directory
structures.
PJ: force gel tool to refresh.
PJ: force cel paste to update when in stream mode.