fix: emsdk swallows/overwrites parts of PATH (#642)

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 #634
Fixes #645

.circleci/config.yml

@@ -87,11 +87,46 @@ jobs:
           command: |
             source emsdk_env.sh
             python scripts/test.py
+
+      - run:
+          name: flagless (process/shell) test
+          shell: powershell.exe
+          command: |
+            scripts/test_activation.ps1
+
       - run:
           name: --permanent test
           shell: powershell.exe
           command: |
-            scripts/test_permanent.ps1
+            $env:PERMANENT_FLAG="--permanent"
+            scripts/test_activation.ps1
+
+      - run:
+          name: --system test
+          shell: powershell.exe
+          command: |
+            $env:SYSTEM_FLAG="--system"
+            scripts/test_activation.ps1
+
+      - run:
+          name: Process/Shell PATH preservation test
+          shell: powershell.exe
+          command: |
+            scripts/test_path_preservation.ps1
+
+      - run:
+          name: User PATH preservation test
+          shell: powershell.exe
+          command: |
+            $env:PERMANENT_FLAG="--permanent"
+            scripts/test_path_preservation.ps1
+
+      - run:
+          name: System PATH preservation test
+          shell: powershell.exe
+          command: |
+            $env:SYSTEM_FLAG="--system"
+            scripts/test_path_preservation.ps1
 
   build-docker-image:
     executor: bionic