xvi should run EXINIT and .exrc unless overridden

xvi is now so complete an implementation that sharing .exrc files with
other vi's is perfectly feasible. We should still check XVINIT and run
only that if it is set, and if not run EXINIT and .exrc files.

POSIX says:

"If the environment variable EXINIT is set, the editor shall execute the ex commands contained in that variable.

If the EXINIT variable is not set, and all of the following are true:
  a. The HOME environment variable is not null and not empty.
  b. The file .exrc in the directory referred to by the HOME environment
     variable:
      i. Exists
     ii. Is owned by the same user ID as the real user ID of the process
	 or the process has appropriate privileges
    iii. Is not writable by anyone other than the owner
the editor shall execute the ex commands contained in that file.

If and only if all of the following are true:
  a. The current directory is not referred to by the HOME environment variable.
  b. A command in the EXINIT environment variable or a command in the .exrc file
     in the directory referred to by the HOME environment variable sets the
     editor option exrc.
  c. The .exrc file in the current directory:
      i. Exists
     ii. Is owned by the same user ID as the real user ID of the process,
	  or by one of a set of implementation-defined user IDs
    iii. Is not writable by anyone other than the owner
the editor shall attempt to execute the ex commands contained in that file.

Lines in any .exrc file that are blank lines shall be ignored.
If any .exrc file exists, but is not read for ownership or permission reasons,
it shall be an error.

After the EXINIT variable and any .exrc files are processed, the first file
specified by the user shall be edited."
