CRM-14439 - CRM_Core_Menu - For breadcrumbs, set forceBackend=1

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* CRM-14439: WP demo - Access denied when visiting breadcrumb links from field listing
  https://issues.civicrm.org/jira/browse/CRM-14439
CRM_Utils_System_WordPress::url - Change code-branch for caes "isset($path)&&isset($query)"

In the other usages of $script and $base, there's a decision to use $script XOR $base as the effective
base-URL.  However, in this branch, the values are concatenated to form the effective base-URL -- which
shouldn't produce a valid base-URL.  (Note: In this context, we're evaluating conditons of isset($path) and
isset($query) which should have no bearing on the validity of $script or $base as a base-URL.)
CRM_Utils_System_WordPress::url - Change code-branch for case "!isset($path)&&!isset($query)"
CRM_Utils_System_WordPress::url - Simplify deep if/else/string-concatenation. Fix forceBackend.
Merge pull request #2859 from totten/4.4-wp-breadcrumb-forceBackend

CRM-14439 - Fix WP breadcrumbs by setting forceBackend=1 and consistently respecting that option