Added FossilDownloadStrategy (Fossil SCM support)
Added FossilDownloadStrategy (Fossil SCM support)

This will enable downloading source repository using fossil SCM.
For example, formulae `fossil` and `mongrel2` can have HEAD version.

Signed-off-by: Adam Vandenberg <34c2b6407fd5a10249a15d699d40f9ed1782e98c@gmail.com>

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