Add *.exe CLEANFILES in Makefile.am.
programs/common.[ch] : Add sfe_endian_name() etc functions.

Functions: sfe_endian_name(), sfe_container_name() and
sfe_codec_name().
programs/sndfile-convert.c : Improve error reporting.

Previous error reporting when the destination audio data format
wasn't supported by the container was inadequate.

Closes : https://github.com/erikd/libsndfile/issues/43