treewide: "require" + "use" cleanup and docs

There's a bunch of leftover "require" and "use" statements we no
longer need and can get rid of, along with some excessive
imports via "use".

IO::Handle usage isn't always obvious, so add comments
describing why a package loads it.  Along the same lines,
document the tmpdir support as the reason we depend on
File::Temp 0.19, even though every Perl 5.10.1+ user has it.

While we're at it, favor "use" over "require", since it it gives
us extra compile-time checking.

1 files changed, 2 insertions, 3 deletions

diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index 8f17f7fb..09dc3992 100644
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -35,9 +35,8 @@ use fields ('sock',              # underlying socket
             'wbuf_off',  # offset into first element of wbuf to start writing at
             );
 
-use Errno  qw(EAGAIN EINVAL);
-use Carp   qw(croak confess carp);
-require File::Spec;
+use Errno qw(EAGAIN EINVAL);
+use Carp qw(confess carp);
 
 my $nextq; # queue for next_tick
 my $WaitPids; # list of [ pid, callback, callback_arg ]