[BUG] relative pillar includes only work in the current directory

[OrangeDog]

Description
Pillars now support relative includes, but only a single level. They should behave the same as state includes.

Steps to Reproduce the behavior

include:
  - .one
  - ..two
  - ...three

Expected behavior
Includes should behave consistently across pillars and states.

Versions Report

salt --versions-report

Salt Version:
           Salt: 3001

Dependency Versions:
           cffi: Not Installed
       cherrypy: Not Installed
       dateutil: 2.6.1
      docker-py: Not Installed
          gitdb: Not Installed
      gitpython: Not Installed
         Jinja2: 2.10
        libgit2: 0.26.0
       M2Crypto: 0.32.0
           Mako: Not Installed
   msgpack-pure: Not Installed
 msgpack-python: 0.5.6
   mysql-python: Not Installed
      pycparser: Not Installed
       pycrypto: 2.6.1
   pycryptodome: 3.4.7
         pygit2: 0.26.2
         Python: 3.6.9 (default, Apr 18 2020, 01:56:04)
   python-gnupg: 0.4.1
         PyYAML: 3.12
          PyZMQ: 17.1.2
          smmap: Not Installed
        timelib: Not Installed
        Tornado: 4.5.3
            ZMQ: 4.2.5

System Versions:
           dist: ubuntu 18.04 Bionic Beaver
         locale: ISO-8859-1
        machine: x86_64
        release: 4.15.0-106-generic
         system: Linux
        version: Ubuntu 18.04 Bionic Beaver

[max-arnold]

@waynew This issue describes the same problem I spotted earlier: #52156 (comment)

[krionbsd]

@OrangeDog thanks for the report, could you please write the patch if it's possible?

[OrangeDog]

No, I have no idea what is the required, nor the time to do it.

[OrangeDog]

Assigning to @waynew, who implemented the original.