Needs to store the version in the file object, since it's only known
after the file is read in, had to make files non-const. Put some checks
in to make sure this isn't abused but pretty messy.
[SVN r75260]
Files are now permanently loaded. Quickbook substrings are stored as
references into the file. Now positions are stored as iterators into
the original file, the line and column is calculated when messages are
output.
This doesn't have much effect on efficiency but it simplifies a few
things.
[SVN r75253]
