Instrument with injected function calls

[cgewecke]

Modifies the instrumentation strategy to use a function call with the instrumentation hash as an argument. This provides a way of getting around 'stack-too-deep' compiler errors which seem more common than initially anticipated. (An initial test on aragon-court triggered many of these.)

Instrumentation now looks something like...

contract Test {
  // Hex identifier postfixes are hashes of the filename 
  function coverage_0xab123(bytes32 c__0xab123) public pure {}

  function a(uint x) public {

    coverage_0xab123(0xdc08f...08ed1); /* function */ 
    coverage_0xab123(0xa9065...549e2); /* line */         
    coverage_0xab123(0x6ac83...f2037); /* statement */ 
  
    if (x == 1) {
  
      coverage_0xab123(0x85e7e...afacf); /* branch */ 
      coverage_0xab123(0xfa262...4fb28); /* line */  
      coverage_0xab123(0xa3e17...38d49); /* statement */ 
  
      x = 3;
  
    } else { 
      coverage_0xab123(0xb54c1...3ef6b); /* branch */ 
    }
}

Gas cost for each instrumentation method call is 13 - possibly small enough make gas distortion a non-issue.

Also added a "stack too deep" test.

[cgewecke]

Hope this ok - the VM reports that both PUSH1 and PUSH2 are called with the same hash at the top of the stack, resulting in duplicate hits. This makes everything contingent on a very specific implementation detail at Solidity though...