Release notes, changelogs, downloads, etc. are available at http://www.x.org/releases/X11R7.5/
E-EDID support (AdamJackson)
Add SELinux security module which uses XACE (EamonWalsh).
RandR 1.3 (KeithPackard)
These are just listed for easy reference here, the above link is the canonical list. Only the release announcement for the version included in X11R7.5 is listed here. Some modules had multiple releases since X11R7.4 - see each module's ChangeLog or git repository for a full list of changes.