Don't set int::config in int::parse_config

This was a bug. Reading more configurations than one would overwrite
int::config.
Don't utilize int:: namespace in int::parse_config

int::parse_config are called very early during init, where the int
namespace isn't yet fully populated. Perhaps this should be indicated
more clearly by moving int::parse_config out of config.tcl and into
init.tcl. I will leave decision that for the future.
Remove get_full_path and use file normalize

We do not need a complicated procedure for this as "file normalize" does
what we want (resolves relative links and aliases like ~).
Add int::root_path to reflect the root directory
Add running config 9pm.rc

A running config for 9pm. Currently containing SSH_OPTS which is passed
to ssh. The user can override the default configuration located in
etc/9pm.rc with its own placed in ~/.9pm.rc which has precedence.