Improve "qmake Function Reference" documentation topic

qmake Function Reference topic (as here http://qt.nokia.com/doc/4.6/qmake-function-reference.html) doesn't mention such conditional functions as equals(), defined(), greaterThan() etc. I've found them only inspecting qmake sources in the repository.

Neither does it mention that count() can receive third parameter that defines comparison operation, as in count(files, 3, greaterThan)

Also, it would save me 20 to 40 minutes if it stated explicitly that first parameter, i.e. variablename when passed to conditional function MUST NOT be prepended by $$ operator. And when comparing two variables, the second one MUST be.