[netsurf-dev] going dynamic with path strings

Hello !

I would like to restore NetSurf in Debian GNU/Hurd, but PATH_MAX is not
defined there. As discussed on IRC, using dynamic allocation for paths
would be a desirable solution, and it is the POSIX way.

Here are the proposed steps in detail :
- Have most of the file-path functions return nserror, as is the
convention in the codebase.
- Stop considering PATH_MAX as an implicit length for static buffers,
and provide the sizes as a parameter instead.
- Switch to dynamic allocation for GTK and framebuffer frontends. Those
are the ones built by Debian.

We could extend this to all the frontends, but let's see how things
go with this series first.

Thanks,

Olivier