Add config framework non-empty string validation requirement option.

Add config framework OPT_CHAR_ARRAY_T and OPT_STRINGFIELD_T non-empty
requirement option.  There are cases were you don't want a config option
string to be empty.  To require the option string to be non-empty, just
set the aco_option_register() flags parameter to non-zero.

* Updated some config framework enum aco_option_type comments.


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@393034 f38db490-d61c-443f-a65b-d21fe96a405b