Add a replacement for reallocarray

Add a replacement for reallocarray for systems (currently anything
that isn't OpenBSD) that don't have it.  This function is the same as
realloc but takes calloc-style arguments and checks for size overflow
before calling realloc.
Add xreallocarray to the util library

Add xreallocarray to the util library, which is a checked version of
reallocarray similar to what xrealloc is for realloc.

Also change the memory thresholds so that the xmalloc test works on
amd64 Debian Linux again.
Bump version numbers of Test::RRA::* Perl modules
Prefer reallocarray to realloc for multiplied sizes
Update to C TAP Harness 3.1

* ok, okv, and is_* now return the success of the test.
* Add breallocarray API for error-checked reallocarray in tests.
* Check for integer overflow on memory allocations.
* Avoid all remaining uses of sprintf.
Prefer bcalloc and breallocarray for space calculations in tests

Use bcalloc instead of bmalloc and breallocarray instead of
brealloc when allocating space determined by a multiplication
in tests.
Update to current version of C TAP Harness 3.1

* diag and sysdiag now return true.
Handle EINTR correctly in network_read and network_write

In network_read and network_write with a timeout, restart the I/O
attempt if a system call failed with EINTR instead of aborting the
operation.
Suppress Kerberos header warnings in make warnings

RRA_LIB_KRB5 and RRA_LIB_KRB5_OPTIONAL now also provide a
KRB5_CPPFLAGS_GCC Makefile variable that can be used in combination
with gcc warnings (such as the make warnings target) to suppress
warnings from Kerberos headers in non-system paths.
Fix xmalloc test skipping if the limit is too low

The introduction of the xreallocarray tests didn't update the way
test skipping was handled with low allocation limits.  Correct that
oversight.
Further increase memory limits for xmalloc tests

When the test program is linked with other libraries, 30MB works
better on amd64 Linux.
Skip the util/messages-krb5 if not built with Kerberos

The util/messages-krb5 test can now be included in a package that may
or may not be built with Kerberos support and will be skipped if
Kerberos support is not enabled.
Release 5.5