[NCF-280]/TLO-836022

Fix bug where leading backslash digit
in name was not being properly handled.
The reason was that I accidentally attemped to allow \x... and \0...
escapes in identifiers. This make identifiers
with leading escaped digits not work any more.
Also added test case.
Merge branch 'master' of https://github.com/Unidata/netcdf-c
Merge branch 'master' of https://github.com/Unidata/netcdf-c
Rebasing