Issues with bbp_replace_the_content()

[johnjamesjacoby]

In some wpcom testing, I uncovered the following issues with bbp_replace_the_content()

• Theme compatibility makes it possible to run the 'the_content' filter inside an existing 'the_content' filter, which results in an infinite loop.
• bbp_replace_the_content() does a global filter remove, which never gets readded.
• Shortcodes do not correctly remove and re-add the 'bbp_replace_the_content' filter.
• We're calling do_shortcode() in the shortcodes, which is also not needed.

[johnjamesjacoby]

(In [3942]) Theme Compatibility:

• Fix issues with 'the_content' and bbp_replace_the_content() causing infinite loops, duplicate filters, no filters, etc...
• Add 'the_content' adds/removes to BBP_Shortcode where needed.
• Remove unneeded calls to do_shortcode().
• Fixes #1844.