Document pkcs12 -password behavior

apps/pkcs12.c accepts -password as an argument.  The document author
almost certainly meant to write "-password, -passin".

However, that is not correct, either.  Actually the code treats
-password as equivalent to -passin, EXCEPT when -export is also
specified, in which case -password as equivalent to -passout.
dlfcn: always define _GNU_SOURCE

We need this for the freebsd kernel with glibc as used in the Debian kfreebsd
ports.  There shouldn't be a problem defining this on systems not using glibc.
Fix various spelling errors
Document openssl dgst -hmac option

I've committed the thing below in MirBSD; since the apps code
changes very little between OpenSSL versions, it will probably
apply to the Debian package as well. I'm open for better wor-
ding though, especially considering the FIPS option, which I
found as undocumented too.
Fix additional pod errors with numbered items.
Use defaults bits in req when not given

If you use "-newkey rsa" it's supposed to read the default number of bits from the
config file.  However the value isn't used to generate the key, but it does
print it's generating such a key.  The set_keygen_ctx() doesn't call
EVP_PKEY_CTX_set_rsa_keygen_bits() and you end up with the default set in
pkey_rsa_init() (1024).  Afterwards the number of bits gets read from the config
file, but nothing is done with that anymore.

We now read the config first and use the value from the config file when no size
is given.

PR: 2592