mogfiledebug: show Last-Modified header if available

This can be useful in several cases:

1) it may be used to determine the original version of the file
   if one copy was corrupted during replication

2) it can also be used to determine when replication congestion
   occurred by comparing the relative differences between
   replicas.
mogfiledebug: add --paths=<print|stat|fetch> option

This allows users to bypass expensive file fetching and
checksumming for large files and/or slow links.
mogadm: improve error message on module load error

On Thu, 6 Jun 2013 19:40:46 -0700, David Birdsong reported
issues to the mailing list about a load failure with mogadm.
Preserve the original $@ error message to hopefully give more
information about failure and aid in diagnosing the problem.
mogadm: do not warn about drain unless drain is specified

Unnecessarily displaying the warning about "drain" is potentially
confusing and scary to new users, especially if they've never
used MogileFS before.
mogadm: include drain devices by default in summary

drain devices are still usable to clients, so it probably makes
sense to include this in the default output of "mogadm device summary"
(especially given the drain change in 2.40)

Not including drain devices by default confused me at first, so
perhaps it may be confusing to others.
mogadm: improve "device list" formatting

With multi-terabyte disks being commong nowadays, the formatting of
"mogadm device list" output has become cramped and hard-to-read.
Additionally, right justifying numeric values makes identifying
order-of-magnitude differences between rows easier:

before:
                   used(G) free(G) total(G) weight(%)
 dev11: alive      1267.246 1483.296 2750.542  100
  dev2: alive      1196.321 637.334 1833.655  100
  dev5: alive      1220.643 154.568 1375.211  100
  dev6: alive      2072.875 677.667 2750.542  100
  dev7: alive      995.188 380.022 1375.211  100

after:

                    used(G)    free(G)   total(G)  weight(%)
  dev11:   alive   1267.246   1483.296   2750.542        100
   dev2:   alive   1196.321    637.334   1833.655        100
   dev5:   alive   1220.643    154.568   1375.211        100
   dev6:   alive   2072.875    677.667   2750.542        100
   dev7:   alive    995.188    380.022   1375.211        100
Checking in changes prior to tagging of version 2.28.

Changelog diff is:

diff --git a/Changes b/Changes
index d7535d7..c3bb0e6 100644
--- a/Changes
+++ b/Changes
@@ -1,3 +1,17 @@
+2.28 -- 2013-08-07
+
+   * mogadm: improve "device list" formatting (Eric Wong <normalperson@yhbt.net>)
+
+   * mogadm: include drain devices by default in summary (Eric Wong <normalperson@yhbt.net>)
+
+   * mogadm: do not warn about drain unless drain is specified (Eric Wong <normalperson@yhbt.net>)
+
+   * mogadm: improve error message on module load error (Eric Wong <normalperson@yhbt.net>)
+
+   * mogfiledebug: add --paths=<print|stat|fetch> option (Eric Wong <normalperson@yhbt.net>)
+
+   * mogfiledebug: show Last-Modified header if available (Eric Wong <normalperson@yhbt.net>)
+
 2.27 -- 2013-01-11

    * mogupload no longer slurps files into memory if the size is known ahead