Update bootstrap.sh.

(cherry picked from commit a63871b7ed005fae265a9e8517e51c346e8c6b5a)

Conflicts:
	cabal-install/bootstrap.sh
More diff friendly pretty printing of cabal files

Added the new field constructor functions 'listFieldWithSep'
and 'commaListFieldWithSep' to be able to define pretty printing
for fields, where each value of the field is positioned on a new line.

Which fields are nested is currently hard coded in the 'ppField' function.

(cherry picked from commit e8d5ea254ab2ed037819bcd094146062ecca7a0b)
Add changelog for Cabal-1.20.0.0
Add changelog for cabal-install-1.20.0.0