support for PostgeSQL 10.0+ #100

Traceback (most recent call last):
  File "/usr/bin/pg_view", line 11, in <module>
    load_entry_point('pg-view==1.4.1', 'console_scripts', 'pg_view')()
  File "/usr/lib/python3.6/site-packages/pg_view.py", line 3474, in main
    postmasters = get_postmasters_directories()
  File "/usr/lib/python3.6/site-packages/pg_view.py", line 3038, in get_postmasters_directories
    postmasters[pg_dir] = [pid, version, dbname]
UnboundLocalError: local variable 'version' referenced before assignment

PG_VERSION_FILENAME:
# cat /proc/<PG PID>/cwd/PG_VERSION
10

fp = open(PG_VERSION_FILENAME, 'rU')
  val = fp.read().strip()
  if val is not None and len(val) >= 3:
      version = float(val)

I do not understand why "len(val) >= 3"
"len(val) >= 1" should be enought.

Unable to read free space information for the pg_xlog and data directories for the directory /pg: [Errno 2] No such file or directory: '/pg/pg_xlog/'
ERROR: 2018-05-24 23:25:55,870 Unable to read free space information for the pg_xlog and data directories for the directory /pg: [Errno 2] No such file or directory: '/pg/pg_xlog/'
Process DetachedDiskStatCollector-1:
Traceback (most recent call last):
File "/usr/lib/python3.6/multiprocessing/process.py", line 258, in _bootstrap
self.run()
File "/usr/lib/python3.6/site-packages/pg_view.py", line 3560, in run
df_data = self.get_df_data(wd)
File "/usr/lib/python3.6/site-packages/pg_view.py", line 3615, in get_df_data
xlog_dev = self.get_mounted_device(self.get_mount_point(work_directory + '/pg_xlog/'))
File "/usr/lib/python3.6/site-packages/pg_view.py", line 3679, in get_mount_point
parent_device = path_device = os.stat(pathname).st_dev
FileNotFoundError: [Errno 2] No such file or directory: '/pg/pg_xlog'