Bug#1069210: dh-elpa: Support nested directory in elpa installation

[Xiyue Deng <manphiz@gmail.com>]

Currently there is a behavior difference between elpafied packages and
upstream ELPA packages on `load-path' handling: for elpafied packages,
all nested directories are added to `load-path', while for upstream ELPA
only the root directory is added.  Normally this should not be an issue,
but when trying to elpafy auctex, it's nested directory "style/"
contains many modules whose names collide with standard modules and
hence broken Eglot.  This sounds like a bad practice of the package, but
it would still be good to match upstream behavior so as to minimize
surprises.  Will try to figure this out.

-- 
Xiyue Deng