MFC: r204665

MFC: r204665

- Make function of finding an available drive name a macro.
- Move check of /dev/ prefix and copy into a function to save code duplication.
  This also fixes a bug where the /dev/ prefix could not be used when creating
  volumes on the command line.

MFC: r209051

Initialize variables before usage.

Found by:	clang static analyzer
Found by:	Coverity Prevent[tm] (CID 7736, 7760)

MFC: r215704

Fix some more warnings found by clang.

MFC: r229915

Fix warning when compiling with gcc46.

git-svn-id: svn://svn.freebsd.org/base/stable/8@266028 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f