Preload internal pages into file system cache with compression.

Previously the functionality only worked without compression enabled.
Add upgrade documentation for new shared_cache configuration option.
Merge branch 'develop' into warm-cache-compress

Conflicts:
	src/include/flags.h
Create a more general-purpose block-manager preload call and pre-load
individual pages instead of using the page locations to guess at the
right file chunks.
Build the connection config stack explicitly, fix a bug where the environment config was appearing at the beginning.
Re-check that calculating an ordinary snapshot hasn't raced with updating the oldest ID.
Merge pull request #559 from wiredtiger/warm-cache-general

Create a more general-purpose block-manager preload call
Another transaction ID fix: ignore the current ID if updating a snapshot during auto-commit.
Merge pull request #538 from wiredtiger/warm-cache-compress

Preload internal pages into file system cache with compression.
remove WT_CONNECTION_IMPL.{msgfile,msgcall}, they're unused.
Merge branch 'develop' into hot-backup