Include password in persistent hash key

[NattyNarwhal]

Matches behaviour of other database extensions, and removes some surprise that the extension doesn't check for a valid password when reusing a connection. Of course, that must be the password the connection was created with, but that's the same for the others too.

Fixes GH-18

XXX: Would like to include options, but not sure how to do this cleanly.

[kadler]

Suggested change

	hKeyLen = strlen(database) + strlen(uid) + strlen(password) + 9;
	hKeyLen = strlen(database) + strlen(uid) + strlen(password) + sizeof("__db2_");

Would be a bit more clear what the 9 means.

[tessus]

Ooops, I've commented on the issue. I'll copy and paste it here as well:

I am not so sure that I like the fact that the password is available in clear text in memory. We don't need a cryptagraphic hash function. Most of the time only one user/password combination is used in web applications.

This is also the reason why I only used a sub string of the hash and not the entire hash back then. e.g. CRC32 is more than enough.

[NattyNarwhal]

Yeah, I found the fact everyone else leaves it out in the open a little surprising (Maybe worth discussing with internals@....). I was going to hash it if it was easy, though I didn't want to vendor/take an additional dependency for something even as trivial as CRC32....

[tessus]

Murmur has about the same collision rate as crc32 and does have an easy implementation:

uint32_t inline MurmurOAAT32 (const char * key)
{
  uint32_t h(3323198485ul);
  for (;*key;++key) {
    h ^= *key;
    h *= 0x5bd1e995;
    h ^= h >> 15;
  }
  return h;
}

uint64_t inline MurmurOAAT64 (const char * key)
{
  uint64_t h(525201411107845655ull);
  for (;*key;++key) {
    h ^= *key;
    h *= 0x5bd1e9955bd1e995;
    h ^= h >> 47;
  }
  return h;
}

I'd just pick either the 32 or 64 bit version and be done with it....

[tessus]

I can change the PR to use murmur, if you want me to.

[NattyNarwhal]

Some missed opportunities, with array hashing, but those can be addressed later. I'd rather have this merged than sitting around.