[1.4.x] Fixed #21248 -- Skipped test_bcrypt if no py-bcrypt found

Pre 1.6 Django worked only with py-bcrypt, not with bcrypt. Skipped
test_bcrypt when using bcrypt to avoid false positives.

Backpatch of 9f8a36eb20895d9e542820d5190bfa77ad1b85d9 from stable/1.5.x.
[1.4.x] Fixed #21256 -- Error in datetime_safe.datetime.combine.

Backport of d9b6fb8 from master
[1.4.x] Fixed #21253 -- PBKDF2 with cached HMAC key

This gives a 2x speed increase compared to the existing implementation.

Thanks to Steve Thomas for the initial patch and Tim Graham for finishing it.

Backport of 1e4f53a6eb8d1816e51eb8bd8f95e704f6b89ead from master.
[1.4.x] Added 1.4.9 release notes

Backport of 2eb8f15516 from master
Fixed #13245: Explained Oracle's behavior w.r.t db_table
and how to prevent table-name truncation

Thanks russellm & timo for discussion, and timo for review.

Backported from master 317040a73b77be8f8210801793b2ce6d1a69301e
[1.4.x] Bumped release date for 1.5.5 & 1.4.9.

Backport of 4ce5c119b5 from master
[1.4.x] Bump everything for 1.4.9 bugfix release.
[1.4.x] Bump version post-release.
[1.4.x] Fixed typo in docs/releases/1.4.9.txt.

Backport of 3b0293370a from master
Fixed SyntaxError on Python 2.5 caused by a @unittest.skipIf class decoration.
Merge pull request #1837 from loic/django14

Fixed SyntaxError on Python 2.5 caused by a @unittest.skipIf class decoration.
Fixed #21362 -- Restored Python 2.5 compatibility.
[1.4.x] Bump version info and add release notes for 1.4.10.
[1.4.x] Added 1.4.10 release notes to index.
Merge branch 'stable/1.4.x' of https://github.com/django/django into stable/1.4.x