Use getExpressionString/getFilterString/getTextString in PHP MapScript

[dmorissette]

In bug 1428 it was pointed out that SWIG MapScript has:

- class.getExpressionString()
- layer.getFilterString()
- label.getTextString()

and PHP MapScript has:

- class.getExpression()
- layer.getFilter()
- missing label.getTextString()

We should synchronize both interfaces in 5.0.

Would it make more sense to add the String suffix in PHP, or to remove it in the
SWIG wrappers? Note that in both SWIG and PHP, the set*() methods don't have the
string suffix (i.e. setFilter(), setExpression(), etc.)

[sdlime]

One correction, getTextString is a class method...

As for naming, I think we chose the string suffix to inform users that it 
wasn't an expressionObj per se, but the string you'd use to build one. That 
probably isn't that important a distinction.

Steve

[dmorissette]

Checking this one...

[dmorissette]

Fixed in r6601: Added class.getTextString() and deprecated/renamed class.getExpression() and layer.getFilter() to class.getExpressionString() and layer.getFilterString() to match what we have in SWIG MapScript