[[ NumberExpectation ]] Added new property to ExecContext, in order to specify when we want to get a number
This avoids a useless number -> ValueRef -> number conversion
[[ Clean up ]] Factor out common code in MCExecContext
[[ Clean up ]] Factor out common EnsureISAllowed code.
Disable building for PPC
Merge branch 'refactor-syntax_unicode' of https://github.com/runrev/livecode into feature-tab_alignments
Merge branch 'refactor-syntax_unicode' into feature-tab_alignments
Rename existing MCSegment to MCLineSegment
Disable existing tab-handling code

Because it hasn't been replaced, tabs do not work at all, currently...
Merge branch 'refactor-syntax_unicode' into refactor-syntax_unicode_number_prediction

Conflicts:
	engine/src/exec.h
[[ Bug 11989 ]] Make sure arrayDecode works on encoded value type empty
Initial support for the segment-based tab system

Still buggy but I'd better commit before I break something...

Outstanding issues:

1. Padding problem with right-aligned text (see script line count in project browser)
2. Crash when opening application browser (related to the grid layout it uses)
3. Not at all tested with RTL text
4. Only slightly tested with LTR text
Fix segments having their horizontal alignment unset
Reduce strings to single backing store
Fix a leak of segment objects
Update the parent pointer of segments when assigned to a different line
Fix segment splitting when doing wrapping
Only add new lines to the parent paragraph once!
Add a function missed in a previous commit
Fix an error with line segmentation
Fix calculation of tab positions