For Java we use the value in the config file so it doesn't need to be in
the PATH.
For python, all our tools should launch via scripts that check for
EMSDK_PYTHON so having python in the PATH for emsdk users should not be
needed.
The motivation for this is that we don't want to clobber any existing
python or java versions that users might already have in their PATH.
This is the easy part of #705.
This PR has three changes:
1) Fixing --permanent flag:
The previous algorithm looped over the values of PATH 4 times to check conditions while these conditions are the opposite of each other. Also, the result did not include all the parts in the whole_path.
I have combined these loops and fixed the algorithm, so no path is lost. Now using --permanent the PATH and Env variables are correctly updated.
2) Fixing --system flag:
Now, the system flag does not cause the PATH values to be overwritten/clobbered. The PATH/Env variables are correctly updated.
3) Fixing flagless flag:
When no flag is provided the value of process/shell is correctly updated and preserved.
This adds the tests for all the situations.
Fixes#634Fixes#645
