Don't try to open files in the distribution for writing

When imported into OpenBSD, this will be attempted to run from a
readonly source tree.  This test fails in that situation because we are
not allowed to open t/truncate_me for writing.

Instead, we can just use the tempfile.
Merge pull request #46 from afresh1/master

Don't try to open files in the distribution for writing
Document GH #46 in Changelog.
Note that the Carp::Always trace isn't always as pretty as we'd like.

Part of GH #34
v2.24

        * FEATURE: Provide a stack backtrace when `Carp::Always` is enabled.
                   Note that sometimes this is not as pretty as it could
                   be, patches welcome.
                   (Thanks to Niels Thykier, GH #35)

        * BUGFIX: Fix situations where `no autodie` doesn't respect lexical
                  scope. (Thanks to Niels Thykier, GH #41, RT #72053,
                  RT #86396)

        * INTERNAL: Remove now unused variables in code (Niels Thykier).

        * DOCS: Make it extra-clear autodie doesn't check `print`.
                (Dave Rolsky, GH #39)

        * TEST: Removed obsolete boilerplate.t

        * TEST / INTERNAL: Enabled travis-ci for Perl 5.8

        * TEST: Stopped some Pod::Coverage tests failing under Perl 5.8

        * BUILD: Better support for building in a read-only directory
                 (courtesy Andrew Fresh, GH #46)
Bump version number after release