Rewrite ProcessConfigFile() to avoid misbehavior at EOF, as per report

Rewrite ProcessConfigFile() to avoid misbehavior at EOF, as per report
from Andrus Moor.  The former state-machine-style coding wasn't actually
doing much except obscuring the control flow, and it didn't extend
readily to fix this case, so I just took it out.  Also, add a
YY_FLUSH_BUFFER call to ensure the lexer is reset correctly if the
previous scan failed partway through the file.