[svn-r337] Changes since 19980403

----------------------

./configure.in
	Moved setting of compiler warning switches earlier in the file.
	Turned on more warning switches to gcc.

./config/linux
	Prints a warning if the gcc version is less than 2.8.1 since
	that version has problems with register allocation for `long
	long'.

./html/Datatypes.html
	Documented sharing of data types between datasets.

./src/H5G.c
./src/H5Gpublic.h
	Implemented H5Gmove(), H5Glink() and H5Gunlink() for hard
	links.  Still have soft links to do.

./src/H5AC.c
./src/H5ACprivate.h
./src/H5D.c
./src/H5E.c
./src/H5Eprivate.h
./src/H5F.c
./src/H5Farray.c
./src/H5Fcore.c
./src/H5Ffamily.c
./src/H5Fistore.c
./src/H5Flow.c
./src/H5Fprivate.h
./src/H5Fpublic.h
./src/H5Fsec2.c
./src/H5Fstdio.c
./src/H5G.c
./src/H5Gent.c
./src/H5Gnode.c
./src/H5Gpkg.h
./src/H5Gprivate.h
./src/H5HG.c
./src/H5HL.c
./src/H5HLprivate.h
./src/H5I.c
./src/H5Iprivate.h
./src/H5MM.c
./src/H5MMprivate.h
./src/H5O.c
./src/H5Oefl.c
./src/H5Oprivate.h
./src/H5Osdspace.c
./src/H5Oshared.c
./src/H5Ostab.c
./src/H5P.c
./src/H5S.c
./src/H5Ssimp.c
./src/H5T.c
./src/H5Tconv.c
./src/H5Tprivate.h
./src/H5Tpublic.h
./src/H5V.c
./src/H5Vprivate.h
./src/H5detect.c
./src/h5ls.c
./test/cmpd_dset.c
./test/dsets.c
./test/external.c
./test/hyperslab.c
./test/iopipe.c
./test/istore.c
./test/shtype.c
./test/tstab.c
	Fixed comparisons between signed and unsigned values. Fixed
	warnings about unused function arguments.

config/linux

@@ -9,6 +9,7 @@
 # Compiler flags. The CPPFLAGS values should not include package debug
 # flags like `-DH5G_DEBUG' since these are added with the
 # `--enable-debug' switch of configure.
+CC=${CC:-gcc}
 
 # What must *always* be present for things to compile correctly?
 CFLAGS="$CFLAGS -ansi"
@@ -18,6 +19,15 @@ CFLAGS="$CFLAGS -ansi"
 DEBUG_CFLAGS="-g -fverbose-asm"
 DEBUG_CPPFLAGS="-DH5F_OPT_SEEK=0 -DH5F_LOW_DFLT=H5F_LOW_SEC2"
 
+case `$CC -v 2>&1 |tail -1 |sed 's/gcc version //'` in
+   2.7.*)
+       echo "You have an old version of gcc, please upgrade to 2.8.1 or better"
+       ;;
+   2.8.*)
+       CFLAGS="$CFLAGS -Wundef -Wsign-compare"
+       ;;
+esac
+
 # What compiler flags should be used for building a production
 # library?
 PROD_CFLAGS="-O3 -finline-functions -malign-double -fomit-frame-pointer"