hp-scan does not escape whitespaces in output file paths

[ce3a]

hp-scan fails opening the pdf output file, if the output file path contains white spaces.

Steps to reproduce the issue:

    cd some/path\ with\ spaces\
    hp-scan -spdf

scan.py seems not to escape spaces in file paths. Fixed locally by changing

    cmd = "%s %s &" % (pdf_viewer, output)

to

    cmd = "%s \"%s\" &" % (pdf_viewer, output)

in several places.

hp-scan version:
  HP Linux Imaging and Printing System (ver. 3.18.3)
  Scan Utility ver. 2.2