further debugging steps

[robert-b]

i am facing memory overwrites. thus is added some glue code to verify read and write addresses within the test code. doing so i couldn't run the test suit anymore - coredumps. so i cleaned up the calling sequence for the low level flash access routines. most test do run again. the one with a failing format and mount call got disabled. and the very last test fails as well.

i have not created a pull request but the code can be found here: https://github.com/robert-b/spiffs

[robert-b]

i introduced two bugs - they got fixed and are comitted.