Round of uvm.h cleanup.

The poorly named uvm.h is generally supposed to be for uvm-internal
users only.

- Narrow it to files that actually need it -- mostly files that need
to query whether curlwp is the pagedaemon, which should maybe be
exposed by an external header.

- Use uvm_extern.h where feasible and uvm_*.h for things not exposed
by it. We should split up uvm_extern.h but this will serve for now
to reduce the uvm.h dependencies.

- Use uvm_stat.h and #ifdef UVMHIST uvm.h for files that use
UVMHIST(ubchist), since ubchist is declared in uvm.h but the
reference evaporates if UVMHIST is not defined, so we reduce header
file dependencies.

- Make uvm_device.h and uvm_swap.h independently includable while
here.

ok chs@

Fix build without DIAGNOSTIC

branches: 1.3.4;
Drop commended out include to a hardcoded path in root's home directory.

branches: 1.2.2;
Make this compile again. From Paul Fleischer.

branches: 1.1.2; 1.1.4;
Import CHFS, which was formerly known as ChewieFS.

CHFS is a file system for flash devices developed by the
Software Engineering Department at University of Szeged, Hungary.

http://chewiefs.sed.hu/

Thanks for all who made it possible.

Fix build without DIAGNOSTIC

Drop commended out include to a hardcoded path in root's home directory.

branches: 1.2.2;
Make this compile again. From Paul Fleischer.

branches: 1.1.2; 1.1.4;
Import CHFS, which was formerly known as ChewieFS.

CHFS is a file system for flash devices developed by the
Software Engineering Department at University of Szeged, Hungary.

http://chewiefs.sed.hu/

Thanks for all who made it possible.

Drop commended out include to a hardcoded path in root's home directory.

branches: 1.2.2;
Make this compile again. From Paul Fleischer.

branches: 1.1.2; 1.1.4;
Import CHFS, which was formerly known as ChewieFS.

CHFS is a file system for flash devices developed by the
Software Engineering Department at University of Szeged, Hungary.

http://chewiefs.sed.hu/

Thanks for all who made it possible.