modernisation of shell.call with shell.new,async_call

commit 5bcf4180

recipe: merge some functions in universal handling

The contents and effects of the functions were identical

commit c99c5204

recipe: only allow concurrent extract for tarballs

Extracting git repos concurrently can result in locking files being hit

commit 9bad1bfa

source: remove unused LocalTarball source class

commit e3f52096

replace some usage of shell.call with shell.async_call

commit 8bfb0f4a

replace some usage of shell.call with shell.new_call