Update calibre to 2.49.0:

New Features

E-book viewer: Add an option to allow only a single book to be viewed at a time. Trying to view a second book will cause it to replace the currently viewed book.
Kobo driver: Add support for the new firmware 3.19.5761
Linux build: Update bundled version of Qt to 5.5.1

Bug Fixes

Fix splash screen getting stuck on OSX when restarting calibre in debug mode
Get Books: Update plugins for various Polish language book stores to handle changes to the website
Amazon metadata download: Handle a change in the amazon website that prevented review metadata from being downloaded
Better algorithm for guessing the 'external' network interface that is displayed to the user
Tag Mapper: Do not allow the user to create rules with invalid regular expressions
E-book viewer: Disallow hyphenation in documents that use mathematical typesetting as the hyphenation breaks that typesetting
E-book viewer: Fix some non-ASCII characters not display in embedded MathML.
Download calibre plugins securely using HTTPS
MOBI Output: Try to autofix corrupted PNG images in the input document.
Nook Glowlight Plus: Send files by default to the NOOK/My Files folder.
E-book viewer: Fix failure to view comic files that contain non-ASCII characters int heir internal filenames.

(wiz)