Prevent further warnings

The algorithm is agnostic to the type of format (1 or 2) it is using. Therefore the compiler thinks there is a possible error. I changed the code where sd2 will be initialized to NULL. Just for killing the compiler warnings and unfortunately one pico second slower ;-)

Also changed the copright statements to the correct year.
Eliminate warning: devargc may be used uninitialized

sr.c:988:16: warning: 'devargc' may be used uninitialized in this function
[-Wmaybe-uninitialized]
Eliminate warning: rc may be used uninitialized

sr.c:677:16: warning: 'rc' may be used uninitialized in this function
[-Wmaybe-uninitialized]
Eliminate warnings when compiling with zlib-1.2.6 or later

In zlib-1.2.6 the definition of gzFile changed from
`typedef voidp gzFile;' to `typedef struct gzFile_s *gzFile;'
which resulted in numerous gcc warnings when compiling sr.c:

sr.c:66:10: warning: assignment from incompatible pointer type [enabled by
default]
sr.c:122:5: warning: passing argument 1 of 'gzwrite' from incompatible
pointer type [enabled by default]
In file included from hstdinc.h:204:0,
                 from sr.c:4:
/usr/include/zlib.h:1324:21: note: expected 'gzFile' but argument is of
type 'struct gzFile_s **'

and similar warnings from MSVC:

sr.c(66) : warning C4047: '=' : 'gzFile *' differs in levels of
indirection from 'gzFile'
sr.c(122) : warning C4047: 'function' : 'gzFile' differs in levels of
indirection from 'gzFile *'
sr.c(122) : warning C4024: 'gzwrite' : different types for formal and
actual parameter 1

After moving the indirection into the definition of the SR_FILE macro,
both zlib-1.2.5 and zlib-1.2.6 (or later) are now supported.
Update pre-requisite levels in bldlvlck

Compilation now requires at least gcc version 3
svn and flex are no longer required
Minimum levels are now specified for grep and m4