[24702] Include key filename in logged message

[24702] Include key filename in logged message

Squashed commit of the following:

commit 593e6bc7e29938ff5c2f7508bde303fb069a97a9
Author: Mukund Sivaraman <muks@isc.org>
Date:   Tue Jun 10 19:17:40 2014 +0530

    Increase size of filename buffers

commit b8685678e026ba98b8833e26664193b6345eb00e
Author: Evan Hunt <each@isc.org>
Date:   Wed Jun 4 18:57:44 2014 -0700

    [rt24702] some tweaks during review

commit adfbc8f808716c63e9e097d92beef104527e5c6f
Author: Mukund Sivaraman <muks@isc.org>
Date:   Wed Jun 4 18:18:35 2014 +0530

    [24702] Include key filename in logged message

commit f1eff77e7e3704b145c3d65101a735467dd81dc3
Author: Mukund Sivaraman <muks@isc.org>
Date:   Wed Jun 4 18:12:43 2014 +0530

    Add dst_key_getfilename()