Python: Don't print warning about PYTHONPATH
Python: Don't print warning about PYTHONPATH

Authors should use `python.standard_caveats` instead.

* Accessor for python.binary
* Made `python.brewed?` more robust if no python found at all
* python.brewed? is more relaxed now and allows older versions
  of the Python formula.
* Only print about wrining sitecustomize.py and distutils.cfg if
verbose and debug.

tonyg/homebrew,hanxue/linuxbrew,pseudocody/brew,MikeMcQuaid/brew,Homebrew/brew,vitorgalvao/brew,claui/brew,palxex/brew,sjackman/homebrew,gordonmcshane/homebrew,konqui/brew,JCount/brew,mahori/brew,AnastasiaSulyagina/brew,DomT4/brew,reitermarkus/brew,reitermarkus/brew,ilovezfs/brew,nandub/brew,DomT4/brew,aw1621107/brew,AnastasiaSulyagina/brew,muellermartin/dist,reelsense/brew,tonyg/homebrew,rwhogg/brew,vitorgalvao/brew,mgrimes/brew,claui/brew,MikeMcQuaid/brew,maxim-belkin/brew,DomT4/brew,sjackman/homebrew,EricFromCanada/brew,Linuxbrew/brew,mahori/brew,amar-laksh/brew_sudo,JCount/brew,reitermarkus/brew,vitorgalvao/brew,bfontaine/brew,gregory-nisbet/brew,mahori/brew,mistydemeo/homebrew,EricFromCanada/brew,MikeMcQuaid/brew,EricFromCanada/brew,Homebrew/brew,hanxue/linuxbrew,aw1621107/brew,muellermartin/dist,Linuxbrew/brew,pseudocody/brew,ilovezfs/brew,palxex/brew,rwhogg/brew,toonetown/homebrew,nandub/brew,gordonmcshane/homebrew,zmwangx/brew,toonetown/homebrew,jmsundar/brew,alyssais/brew,mistydemeo/homebrew,zmwangx/brew,Linuxbrew/brew,aw1621107/brew,JCount/brew,Homebrew/brew,staticfloat/brew,zmwangx/brew,claui/brew,amar-laksh/brew_sudo,mistydemeo/homebrew,Linuxbrew/brew,amar-laksh/brew_sudo,konqui/brew,bfontaine/brew,vitorgalvao/brew,pseudocody/brew,alyssais/brew,nandub/brew,konqui/brew,claui/brew,ilovezfs/brew,sjackman/homebrew,hanxue/linuxbrew,AnastasiaSulyagina/brew,EricFromCanada/brew,DomT4/brew,Homebrew/brew,muellermartin/dist,jmsundar/brew,palxex/brew,MikeMcQuaid/brew,reelsense/brew,rwhogg/brew,nandub/brew,bfontaine/brew,toonetown/homebrew,alyssais/brew,staticfloat/brew,jmsundar/brew,gregory-nisbet/brew,maxim-belkin/brew,staticfloat/brew,sjackman/homebrew,reitermarkus/brew,tonyg/homebrew,mgrimes/brew,konqui/brew,mgrimes/brew,maxim-belkin/brew,gregory-nisbet/brew,reelsense/brew,gordonmcshane/homebrew,mahori/brew,JCount/brew