Update to 52.9.1

Changelog:
    changed
    Thunderbird will now prompt to compact IMAP folders even if the account is online. Note: Under certain circumstances an incorrect estimate of the expected gain is shown.

    fixed
    Complete fix of the EFAIL vulnerability: 1) Removing some HTML crafted to carry out an attack. 2) Optionally: Not decrypting subordinate message parts that otherwise might reveal decrypted content to the attacker. Preference mailnews.p7m_subparts_external needs to be set to true for added security.

    fixed
    Various problems when forwarding messages inline when using "simple" HTML view

    fixed
    Deleting or detaching attachments corrupted messages under certain circumstances (not working only in Thunderbird version 52.9.0)

    fixed
    Various security fixes

Security fixes:
#CVE-2018-12359: Buffer overflow using computed size of canvas element
#CVE-2018-12360: Use-after-free when using focus()
#CVE-2018-12372: S/MIME and PGP decryption oracles can be built with HTML emails
#CVE-2018-12373: S/MIME plaintext can be leaked through HTML reply/forward
#CVE-2018-12362: Integer overflow in SSSE3 scaler
#CVE-2018-12363: Use-after-free when appending DOM nodes
#CVE-2018-12364: CSRF attacks through 307 redirects and NPAPI plugins
#CVE-2018-12365: Compromised IPC child process can list local filenames
#CVE-2018-12366: Invalid data handling during QCMS transformations
#CVE-2018-12368: No warning when opening executable SettingContent-ms files
#CVE-2018-12374: Using form to exfiltrate encrypted mail part by pressing enter in form field
#CVE-2018-5188: Memory safety bugs fixed in Firefox 60, Firefox ESR 60.1, Firefox ESR 52.9, and Thunderbird 52.9

(ryoon)