[Migrations] assert protobuf-c, json-c, fstrm packages available before applying October migration.

[Bootstrapper] Package scripts may pass "yum_transaction_hook" variable to inform Bootstrapper if scripts are running from within Yum transaction. Resolves a potential deadlock if an included tag calls yum during transaction.
[PHP] Automate recovery if apache,webuser system user is missing from /etc/password.
[UI] "Use External Opener" feature always appends to URLs that match ^http.
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