I've added --section-name, --parameter-name, and --show-all-parameters to
testparm to make it handier for the daily usage.

--section-name allows to limit the view of testparm to one section.  If
you use global it shows the global section.

--parameter-name allows to limit the view to one parameter.  If the
section name isn't set global is assumed.

--show-all-parameters outputs a ini file with [local] and [global]
sections of all available parameters, the type, possible values for
enums, and the flags. For example:

ldap ssl=P_ENUM,no|No|off|Off|start tls|Start_tls,FLAG_ADVANCED

This might allow a configuration tool to provide appropriate control
widgets for each parameter.  We'll create this list while the build
process and ship it with the Samba package.