Fix typo in file filter.

Must have 2 filters srcsupported and srcincluded.
Add word separator attribute to the LineReader class.

Words are split at whitespace when the separator string is empty.
When single character, use it as a word delimiter.
Add function bcneutron for coherent scattering lengths.

bcneutron loads neutron data from a runtime table.
Replace class SFTperiodictable with SFTNeutron.

Refactored to a new class that looks up values in runtime data.
No dependence on the periodictable package anymore.
Update names of test methods.
Do not use the unsupported strip "-s" flag on MacOSX.
Allow build customization via sconscript.local.