[R-sig-Debian] broken dependencies on 2cd4u

[Jeroen Ooms]

As of a few days I'm seeing this error on travis:

The following packages have unmet dependencies:
 libleptonica-dev : Depends: liblept5 (= 1.74.4-1+nmu1ppa1~trusty1)
but it is not going to be installed

Which is caused by:

The following packages have unmet dependencies:
 liblept5 : Depends: libopenjp2-7 (>= 2.0.0) but it is not installable

This is caused by the recent update libleptonica on c2d4u. I guess
this new version also requires a backport of libopenjp2-7.

More generally I'm wondering if perhaps c/c++ libs backports should go
into a separate PPA? I was assuming c2d4u would only provide r-cran
packages but not have any side effects on system libs.