Escape { and } in regexes when used as literals

Perl 5.17.6 (on the path to 5.18) deprecates and warns quite noisily
about unescaped braces.  RT's dependency chain isn't fully clean of this
warning, however...
File::Temp under 5.18 warns if passed an undefined template

File::Temp does not require that a defined template be provided -- if an
even number of arguments is passed, an undef template is assumed.  This
has been true for all versions of File::Temp, so does not break
backcompat.

Explicitly passing an undef template causes "Use of uninitialized value
$_[0] in string eq" warnings on 5.18, so skip doing so.
REST fix: show updated message as long as the object is updated.

previously, we only check if the last update succeeded or not, which is not
that right.

without this, t/web/command_line.t will fail on perl 5.18.0 because of the new
*random* results of hash's keys().
compare ref type first to make sure $entry_ref is not weirdly overloaded

one snippet:

    use Math::BigInt;
    no strict 'refs';
    # $round_mode = bless( do{\(my $o = 'even')}, 'Math::BigInt' );
    my $round_mode = *{'Math::BigInt::round_mode'}{SCALAR};
    print 'ok' if $round_mode;

because Math::BigInt overloads "bool" operation, the "if $round_mode" dies
with message "Not a HASH reference".

we do similar GLOB thing in RT::Config::__GetNameByRef, but before perl 5.18,
we can always find the right Name before checking "Math::Big::Int::round_mode"
thanks to the consistent hash's keys() behavior.

hash's keys() behavior has been changed since perl 5.18:

   Hash randomization
    The seed used by Perl's hash function is now random. This means that the
    order which keys/values will be returned from functions like "keys()",
    "values()", and "each()" will differ from run to run.

i.e. we might reach "Math::Big::Int::round_mode" in RT::Config::__GetNameByRef
since perl 5.18, so we need to make sure it won't die, that's the reason we do
the extra check before the "bool" operation("next unless $entry_ref;")

Math::BigInt is require by GnuPG::Interface.
Merge branch '4.0/perl-5.18-compat' into 4.0-trunk