Heartbleed bug warning should not cause test failure

The feedback I received to the idea of causing a test failure if the version
of OpenSSL against which Crypt::SSLeay was being built might be vulnerable
to the Heartbleed bug indicated that it is better to just warn.

While it there is ready made code that can be used for an exact test of
Heartbleed vulnerability, I am not sure how to incorporate that into the
build. The ways I can think of cause such test code to be added to this
module's dynamically loaded library, and it doesn't seem wise to me to put
such test code there.

Also, removed `openssl_hex_version` from Crypt::SSLeay::Version. Now, we
have `openssl_version_number` which just returns the OPENSSL_VERSION_NUMBER
defined in `crypto/opensslv.h`.

Updated test files to reflect changes.
Include version api changes missed in previous commit
Update manifests, add relevant test scripts
Delay showing 'do you need Crypt::SSLeay'

Previously, we were filtering the libs list right after showing this message
which caused a delay as Devel::CheckLib went through the motions which might
cause the person who's building the module to be concerned.

Instead, show warning after libs have been filtered.
Use ERR_get_error_string_n to avoid buffer-overflow

The `ERR_get_error_string` function which has been in `SSLeay.xs` since
before I started maintaining this module was using ERR_get_error_string with
a local char array. Instead, use ERR_get_error_string_n which allows passing
the size of the array.
Use a define'd constant rather than sizeof

In `SSL_CTX_new`, if loading from `/dev/urandom` fails, the contents of a
local char array is used as a seed source. The size of this memory block is
passed using sizeof, but if the argument was ever changed to be `char *`,
this would not be good. So, instead, use a define'd constant.
Check RAND_load_file failure correctly

According to http://wiki.openssl.org/index.php/Random_Numbers#Initialization
you check for failure by comparing bytes read to bytes requested, not by
checking if the return value is negative.
Use new name for OpenSSL_add_all_algorithms

`SSLeay_add_all_algorithms` was renamed to `OpenSSL_add_all_algorithms`.
While this does not break the code, it makes it hard to remember where to
look up documentation, so use the new name.
const qualify some pointers, use define'd length for buffer