[BusyBox] gunzip cleanup

[Glenn McGrath]

Busybox with nothing defined
-rwxr-xr-x    1 root     bug1         5820 Mar 11 12:03 busybox
   text	   data	    bss	    dec	    hex	filename
   4015	    340	     40	   4395	   112b	busybox

With current gunzip defined
-rwxr-xr-x    1 root     bug1        16828 Mar 11 12:02 busybox
   text	   data	    bss	    dec	    hex	filename
  14512	    828	   1204	  16544	   40a0	busybox

With my gunzip modified code
-rwxr-xr-x    1 root     bug1        14500 Mar 11 12:01 busybox
   text	   data	    bss	    dec	    hex	filename
  12194	    840	     88	  13122	   3342	busybox

So the current gunzip adds 11008B, new modified gunzip 8680B, and the
new code reduces bss size.

Some changes include
 - Use stream buffered input rather than internal buffering on low level
input.
 - Use getopt.
 - Remove nearly all remaining defines.
 - Independed from gzip.c (some functions will need to be moved to
gzip.c
 - FILE *gz_open(FILE *compressed_file) function (base on code from bb
tar -z initialisation)

Some preliminary speed tests indicate it may be upto 10% slower, but im
getting some inconsistent numbers.. so ill have to do more tests on that
and try and tweak it.

I did start cleaning up gzip.c as well, reduced the source code from
100kB to about 60kB, the existing code is really messy, but ive stuffed
it up and doesnt work now..... damnit :(

Anyway, the gunzip code is looking ok, probably still some minor things
to fix up, i will wait till the dust settles post 0.50 before thinking
about commiting, untill then if anyone wants a look let me know.


Glenn