Replaced another typedef (shared_ptr<ISampleBuilder>).

This will allow us to notify the parent about changed parameter values.
Accompanying changes and problems:
- The default constructor ParameterPool() is deleted, to enforce
  presence of a parent.
- Therefore several tests had to be outcommented (marked as
  TEMPORARILY DISABLED). Improved tests should make more
  realistic use of ParameterPool, providing it an IParameterized* parent.
- The function IParameterized::getParameters() is outcommented.
  It was only used in some tests, and for printout. In printout
  functions, it is temporarily replaced by fixed text.

expand parameter_t (no typedef as alias for lengthy class names, except perhaps ocasionally at file scope)

improves the accuracy near q=0.
This closes issue 1401.

plot_diff script: compute change relative to average of old and new.

Test of precomputed factorial vs tgamma outcommented because tgamma is too unprecise under glibc 2.12. Instead, test 150! vs value from Wolfram Alpha.