Prepare for a new netpgp-20091210 portable release.

Apart from infrastructure changes, there are the following functional ones:

+ Update to version 20091210

+ provide a new netpgp_match_list_keys(3) function to perform a
regular-expression based search of all the keys in the keyring.  If no
pattern is specified to match, then all keys are returned.

+ provide a new netpgp_set_homedir(3) function, and use it to set the
home directory from the library, rather than individually in all the
programs which use the library

+ provide a new netpgp_incvar(3) function which will add a constant
increment (which may be negative) to the value of an internal
variable.  This is primarily used for the verbosity level within the
library, and is again a movement of the function into the library from
the individual programs which use the library

+ move to the specification of an ssh key file by internal variable,
rather than the directory holding an ssh key file

+ autoconf infrastructure changes

+ take a hammer to the _GNU_SOURCE definitions problems

+ don't rely on strnlen(3) being present everywhere

(agc)