yaml loading with source code position marking
WIP on spec/parser
spec.parser -> spec.package
topological_stage_sort
start on assembly of build script
Change environment variable $SOMEPKG to $SOMEPKG_DIR
spec.utils.substitute_stack_parameters
profile parameter substitution in assembled build script
fixup of core.test.utils.dump
create_build_spec; substitute_{stack,profile}_parameters
Change hash function: Hash serialized JSON rather than self-defined serialization

Also removes any nohash_ keys before serialization.
run_job: Support nohash_value for setting environment variables in build.json
marked_yaml_load: Support loading integers as int_node
fixup for core.hasher tests
fixes to core.test.utils
more tests for spec.package
Initial work on profile; supports extending profiles on local filesystem
'packages' section in profiles
Merge branch 'master' into spec
spec.profile: Support loading base profile from git repo