Support suppressed errors using "@" to ignore exceptions

[tomlongridge]

Goal

Exception reporting can be suppressed for an expression by prefixing it with the error control operator "@". This is correctly ignored by the notifier if the error reporting level is not configured in the library but it is not suppressed if an error reporting level has been configured.

The PHP documentation states that custom error handlers:

can (and should) call error_reporting()

Therefore this change ensures that suppressed errors are always ignored and not reported to Bugsnag.

Changeset

Changed

• Configuration - amended shouldIgnoreErrorCode to return true in all cases if the error is suppressed (i.e. error_reporting() returns 0).

Tests

Added extra tests for this functionality - including mocking the error_reporting global function.

Linked issues

Fixes bugsnag/bugsnag-wordpress#35.

Review

For the submitter, initial self-review:

• Commented on code changes inline explain the reasoning behind the approach
• Reviewed the test cases added for completeness and possible points for discussion
• A changelog entry was added for the goal of this pull request
• Check the scope of the changeset - is everything in the diff required for the pull request?
• This pull request is ready for:
  • Initial review of the intended approach, not yet feature complete
  • Structural review of the classes, functions, and properties modified
  • Final review

For the pull request reviewer(s), this changeset has been reviewed for:

• Consistency across platforms for structures or concepts added or modified
• Consistency between the changeset and the goal stated above
• Internal consistency with the rest of the library - is there any overlap between existing interfaces and any which have been added?
• Usage friction - is the proposed change in usage cumbersome or complicated?
• Performance and complexity - are there any cases of unexpected O(n^3) when iterating, recursing, flat mapping, etc?
• Concurrency concerns - if components are accessed asynchronously, what issues will arise
• Thoroughness of added tests and any missing edge cases
• Idiomatic use of the language