Merge branch '6.11.6' into no-libpng
Remove bundled-in "libpng" package.
v6.11.6.8
Removed "libpng" from LDM library makefile.
v6.11.6.9
Removed lint(1).
Enhanced verification of GRIB2 message structure.
Removed lint(1).
Added "-v|-x" option and some debug-level messages .
Removed Laraine from the set of testing hosts.
v6.11.6.10
Ensured that LIBS references the math library if necessary.
v6.11.6.11
Corrected "png.h" inclusion.

Changed "libpng.h/png.h" to just "png.h" and added "/user/sfw/include"
to "png.h" search-path.
More "png.h" corrections.
Converted LDADD in program Makefile.am-s to <program>_LDADD.
v6.11.6.12
Added "/usr/local/lib" after some "/opt/lib" searches.
Eliminated removal of test-directory.
v6.11.6.13