[QScintilla] mk_distinfo.py: wrong logic for INSTALL_ROOT installations

[Davide Pesavento]

Hi,

I'm installing QScintilla with 'make INSTALL_ROOT=/foo/bar install'
and the mk_distinfo.py step fails while trying to open non-existent
files, e.g.:

Traceback (most recent call last):
  File "mk_distinfo.py", line 101, in <module>
    fn_f = open(fn, 'rb')
FileNotFoundError: [Errno 2] No such file or directory:
'/usr/lib/python3.7/site-packages/PyQt5/Qsci.so'

(the file is actually at /foo/bar/usr/lib/python3.7/site-packages/PyQt5/Qsci.so)

I took a quick look at the build system and noticed that the file
paths in installed.txt are not prefixed with INSTALL_ROOT.
Unfortunately that file is generated at configure time, when
INSTALL_ROOT is not yet known, so this part of the build process may
require a redesign.

Thanks,
Davide