fetch : throw error when ahead commit and introduce --force flag
fetch : throw error when ahead commit and introduce --force flag

return an error that fetch is not allowed when there is ahead commits in bare repository
and introduce a flag --force which, when used, do fetch anyway and loose the ahead commits

irontoby/git-tfs,NathanLBCooper/git-tfs,git-tfs/git-tfs,TheoAndersen/git-tfs,WolfVR/git-tfs,adbre/git-tfs,hazzik/git-tfs,allansson/git-tfs,allansson/git-tfs,guyboltonking/git-tfs,modulexcite/git-tfs,hazzik/git-tfs,bleissem/git-tfs,TheoAndersen/git-tfs,PKRoma/git-tfs,guyboltonking/git-tfs,vzabavnov/git-tfs,irontoby/git-tfs,andyrooger/git-tfs,modulexcite/git-tfs,adbre/git-tfs,steveandpeggyb/Public,kgybels/git-tfs,NathanLBCooper/git-tfs,codemerlin/git-tfs,bleissem/git-tfs,jeremy-sylvis-tmg/git-tfs,hazzik/git-tfs,bleissem/git-tfs,allansson/git-tfs,WolfVR/git-tfs,codemerlin/git-tfs,irontoby/git-tfs,adbre/git-tfs,TheoAndersen/git-tfs,NathanLBCooper/git-tfs,pmiossec/git-tfs,modulexcite/git-tfs,steveandpeggyb/Public,steveandpeggyb/Public,kgybels/git-tfs,kgybels/git-tfs,codemerlin/git-tfs,guyboltonking/git-tfs,hazzik/git-tfs,allansson/git-tfs,WolfVR/git-tfs,TheoAndersen/git-tfs,jeremy-sylvis-tmg/git-tfs,jeremy-sylvis-tmg/git-tfs