[GRASS5] Imagery GROUP file

[Glynn Clements]

The use of the name "GROUP" for file which stores the current imagery
group conflicts with the "group" directory on filesystems which
perform case folding.

Someone has added a fix specifically for Cygwin:

	#ifdef __CYGWIN__
	#define GROUPFILE "CURGROUP"
	#else
	#define GROUPFILE "GROUP"
	#endif
	
	#ifdef __CYGWIN__
	#define SUBGROUPFILE "CURSUBGROUP"
	#else
	#define SUBGROUPFILE "SUBGROUP"
	#endif

However:

1. The same problem may occur with MacOS X, where case-folding
filesystems are not uncommon.

2. Users of conventional Unices might access a GRASS database which is
stored on a case-folding filesystem, e.g. an SMB share which is used
by both Unix and Windows systems, or a FAT partition on a dual-boot
Linux/Windows box.

3. This creates a portability problem regarding distributed datasets
(e.g. the "imagery" dataset, which includes a GROUP file).

Consequently, I've changed the definitions so that the files are
always called CURGROUP and CURSUBGROUP.

Users will need to rename (or re-create) any GROUP/SUBGROUP files
after updating to the new code.

Also, any supplied datasets (e.g. "imagery") will need to be updated.

-- 
Glynn Clements <glynn.clements at virgin.net>