General code clean-up

[johnjamesjacoby]

Went hunting through trunk last night, and see some areas where code can be improved.

• Use wp_parse_id_list() where appropriate
• Use implode() instead of join() alias
• Audit cache keys for correctness
• Use strict false comparison for wp_cache_get() results
• Improve $post_status array building, since it happens so frequently

[johnjamesjacoby]

In 4896:

Use implode() instead of join() through-out project. See #2331.

[johnjamesjacoby]

In 4897:

Delete the correct 'bbpress_users' cache group for subscriptions and favorites. See #2331.

[johnjamesjacoby]

In 4898:

Cache clean-up:

• Perform strict comparisons on wp_cache_get() results.
• Add caching to bbp_get_topic_favoriters().
• Use wp_parse_id_list() where appropriate in touched functions.
• See #2331.

[johnjamesjacoby]

In 4899:

Query clean-up:

• Move implode() calls out of queries and replace with variables.
• Audit IN queries and implode/explode for wp_parse_id_list() usages.
• See #2331.

[johnjamesjacoby]

In 4900:

Improve micro-performance of favorites and subscriptions by moving function calls after sanity checks. Also typecast the return value of respective get_topic_ids functions. See #2331.

[johnjamesjacoby]

All of the issues in the ticket are addressed. Resolving as fixed.