check public release is global

[johndonor3]

The check_public_release is a global function, and it always uses the release date from the tree as set when Access() is instantiated.

from sdss_access.path.path import check_public_release, Path
from sdss_access import tree

a = Path(release='dr18')
tree
Tree(sas_base_dir=/Users/brian/Work/sdss/sas, config=dr18, release=DR18)

check_public_release('DR15')
True

check_public_release('DR19')
True

a = Path(release='dr19')
tree
Tree(sas_base_dir=/Users/brian/Work/sdss/sas, config=dr19, release=DR19)

a=Path(release='dr19')

check_public_release('DR15')
False

check_public_release('DR19')
False