Fix HP-UX build support

Rename hpux10.exports to hpux.exports.  In the HP-UX section of
shlib.conf, remove '+s' because it just specifies a default, add a
MAKE_SHLIB_COMMAND, and set SHLIBEXT based on the host CPU.

[ghudson@mit.edu: squashed commits, condensed commit message]

ticket: 7990 (new)
target_version: 1.13
tags: pullup