gcry_md_open() may return NULL in case of an unknown algorithm

Return GCRYERR_NOMEM instead of using m_alloc in most library functions

SCO UnixWare/7.1.0  reported by Allan Clark <allanc@sco.com> for 0.9.8


Some other reported cpu-vendor-os strings:

    hppa1.1-hp-hpux10.20
    mips-sgi-irix6.2
    sparc-sun-solaris5.4
    sparc-sun-sunos4.1.2
    i386-pc-sysv4.2   (USL Unixware v1.1.2)


Johan Wevers <johanw@vulcan.xs4all.nl> is working on a NL translation.