[BusyBox] gunzip.c cleanups

[Glenn McGrath]

Ive done some cleanups on gunzip.c which i will commit in a minute.

Its mostly superficial, like
	reducing the multiple copyright statements down to just one,
	removing defines that wernt used (i hope i didnt make a mistake with
this)
	grouping all includes, defines and global variables up the top,
	reorganising the layout so functions dont have to be declared

It reduces the source code size by about 40%, it should be a lot more
readable now.

One programming change i did make was to remove the static crc table,
instead it generates the table which saves about 1KB, not much, but
still smaller the better i assume.

Ive done some light testing and cant see any problems with it.

I did have a go a building a gunzip based on zlib, it ended up about 4KB
bigger than the existing bb gunzip.c, so i figured its better to fix up
the existing code.


Glenn