Refactored xsltValueOf(). Changed to use xmlXPathCastToString() directly,

Refactored xsltValueOf(). Changed to use xmlXPathCastToString() directly,

* libxslt/attributes.c libxslt/documents.c
  libxslt/functions.c libxslt/keys.c libxslt/namespaces.c
  libxslt/pattern.c libxslt/preproc.c libxslt/templates.c
  libxslt/templates.h libxslt/transform.c libxslt/variables.c
  libxslt/xslt.c libxslt/xsltInternals.h libxslt/xsltutils.c
  libxslt/xsltutils.h libexslt/common.c libexslt/dynamic.c
  libexslt/functions.c libexslt/strings.c:
  Refactored xsltValueOf(). Changed to use xmlXPathCastToString()
  directly, rather than creating an intermediate object with
  xmlXPathConvertString(). This now does not add a text-node to
  the result if the string is empty (this has impact on
  serialization, since an empty text-node is serialized as
  <foo></foo>, and now it will be serialized as <foo/>).
  Refactored other functions in transform.c:
  Mostly code cleanup/restructuring. Minimized number of
  function variables for instruction which eat up function stack
  memory when recursing templates (xsltIf(), xsltChoose(),
  xsltApplyTemplates(),  xsltCallTemplate()).
  Changed XSLT tests to use xmlXPathCompiledEvalToBoolean().
  Implemented redefinition checks at compilation-time and
  eliminating them at transformation time in the refactored code
  paths.
  Introduced the field @currentTemplateRule on xsltTransformContext to
  reflect the "Current Template Rule" as defined by the spec.
  NOTE that ctxt->currentTemplateRule and ctxt->templ is not the
  same; the former is the "Current Template Rule" as defined by the
  XSLT spec, the latter is simply the template struct being
  currently processed by Libxslt.
  Added XML_COMMENT_NODE and XML_CDATA_SECTION_NODE to the macro
  IS_XSLT_REAL_NODE.
  Misc code cleanup/restructuring and everything else I already forgot.
  Refactored lifetime of temporary result tree fragments.
  Substituted all calls to the now deprecated xsltRegisterTmpRVT()
  for the new xsltRegisterLocalRVT().
  Fragments of xsl:variable and xsl:param are freed when the
  variable/pram is freed.
  Fragments created when evaluating a "select" of xsl:varible and
  xsl:param are also bound to the lifetime of the var/param.
  EXSLT's func:function now uses the following functions to let take
  care the transformation's garbage collector of returned tree
  fragments:
    xsltExtensionInstructionResultRegister(),
    xsltExtensionInstructionResultFinalize()
  Fixes:
  #339222 - xsl:param at invalid position inside an xsl:template is
            not catched
  #346015 - Non-declared caller-parameters are accepted
  #160400 - Compiles invalid XSLT; unbound variable accepted
  #308441 - namespaced parameters become unregistered
  #307103 - problem with proximity position in predicates of match
            patterns
  #328218 - problem with exsl:node-set() when converting strings
            to node sets
  #318088 - infinite recursion detection
  #321505 - Multiple contiguous CDATA in output
  #334493 - "--param" option does not have root context
  #114377 - weird func:result/xsl:variable/exsl:node-set interaction
  #150309 - Regression caused by fix for 142768