Removed the .gz, .Z, .sz etc suffix searching when looking for reference files.

These are a hang-over from the Staden Package io_lib
days, but did not function correctly in htslib anyway as we had
already removed the decompression code (plus it was inappropriate for
http requests to boot).
Remove the | from the default REF_PATH.

Although this is still syntacally considered legal by the code, it has
no effect and so this may just lead to confusion by the reader.
bgzf: Write plain gzip files if is_gzip set
bgzf_open(..,"g") for compressed gzip output, as opposed to BGZF