d-conf profile parser has painful line-length bug

[Thomas Bushnell, BSG]

In engine/dconf-engine.c, the parser in dconf_engine_load_profile has a seekrit requirement that profile lines be less than eighty characters long, and generates an abort if it finds a longer line.

This is entirely undocumented.

For lines which specify databases, this establishes an entirely undocumented limitation on the length of the filenames for databases (much much less than the system limit). If it cannot be fixed (but really, it can easily be fixed), then the limitation needs to be documented.

Worse, the line-length limitation is applied even to comment lines. That causes a disaster for sites which use version-control identity strings. Such strings are often the most important reason for a comment in a file like this, and often expand to quite long pathnames. Because the limitation is not documented at all, it is easy to test that comments in this file work (they do), and not see a problem until code is checked in and the version control system expands the comment into something more than eighty characters long. Fixing this is even more important than fixing it for lines which specify databases, actually.