Fix one subprocess call that neglected to use $MAKE to override "make".
(On FreeBSD we need to use "gmake" instead.)

Cython recently added __pyx_CommonTypesMetaclass_get_module() but
neglected to make it static; cf cython/cython#6957. Remove it from
the lists of defined symbols to be checked for collisions.

Also ensure that we only strip one leading underscore on macOS,
so that this function's name is as expected.

Rearrange so that KSTREAM_INIT/KSEQ_INIT is used only in *.pyx files
rather than *.pxd headers, so that the functions don't pollute other
extension modules. Declare only the needed types in the *.pxd headers.

Remove kstream_t, so <htslib/kseq.h> is used only by libcfaidx.pyx.

c{sam,bcf}tools_util.h are long since replaced by {sam,bcf}tools.pysam.h.
Only this commented-out libctabix.pyx code used getline(), so remove its
fallback definition in pysam_utils.c and hence remove the now-empty
pysam_util.[ch]. Remove unused header inclusions from htslib_util.c.

…ormat

Prevents "Casting a GIL-requiring function into a nogil function" warnings.

We need to search /usr/local/include to find curl/curl.h etc.
However it needs to be searched AFTER ./htslib et al so that pysam
is compiled against headers from ./htslib/htslib/*.h rather than
any system-installed HTSlib headers in /usr/local/include.