Since we switched from autotools to Meson in commit
94592c14, we don't need to include
`config.h` early to properly enable large file support.  Meson passes
the required macros on the compiler command line instead of defining
them in `config.h`.

This means we can include `config.h` at any time, whenever we want to
check its macros, and there are no ordering constraints.

Replaces GLib's GError.

Replace g_strchug() calls with a cheaper implementation.

After we've been hit by Large File Support problems several times in
the past week (which only occur on 32 bit platforms, which I don't
have), this is yet another attempt to fix the issue.

Allow most printable characters in unquoted words.  The tokenizer
patch introduced very strict requirements for command parameters -
those were undocumented, and we're reverting the strictness now.

The new code is more robust and more flexible.  It provides detailed
error information in GError objects.