Trivial updates to Testing documentation (#336)

* Documentation & comment updates.

* test/test-config-example.jam
    (Comment): Changed 'test-system.jam' to 'test-config.jam'
    - Consistency with doco elsewhere & code in 'test/BoostBuild.py'.

* test/test_system.html
    Updated instructions to reflect broken Python2 compatibility
    ( 9a96cba - "test_all.py", line 97: s = f"\r{s}" )
   and spelling fixes.

* Trivial syntax error in template.

* test/template.py
    (main): Missing closing bracket.

test/template.py

@@ -21,7 +21,7 @@
 
 t.write("hello.cpp", """
 int main() {}
-"""
+""")
 
 # Run the build.
 t.run_build_system()

test/test-config-example.jam

@@ -4,7 +4,7 @@
 
 
 # Skeleton for test configuration. If your local configuration
-# interferes with testing, rename this files to 'test-system.jam'
+# interferes with testing, rename this file to 'test-config.jam'
 # and tweak it. When tests are run, only this file will be loaded,
 # while site-config.jam and user-config.jam will be ignored.
 

test/test_system.html

@@ -94,8 +94,8 @@ <h1>A testing system for B2<br class="clear">
     <h2><a name="sec-intro">Introduction for users</a></h2>
 
     <p>The testing system for B2 is a small set of Python modules and
-    scripts for automatically testing user-obversable behaviour. It uses
-    components from testing systems of <a href="http://www.scons.org">Scons</a>
+    scripts for automatically testing user-observable behaviour. It uses
+    components from testing systems of <a href="http://www.scons.org">SCons</a>
     and <a href="http://subversion.tigris.org">Subversion</a>, together with
     some additional functionality.</p>
 
@@ -105,8 +105,8 @@ <h2><a name="sec-intro">Introduction for users</a></h2>
       <li>Get the source tree of B2 (located at <tt>tools/build</tt>
       in Boost)</li>
 
-      <li>Have <a href="http://www.python.org">Python</a> installed. Version
-      2.1 is known to work.</li>
+      <li>Have <a href="http://www.python.org">Python 3</a> installed. Prior
+      versions are no longer compatible.</li>
 
       <li>Build Boost.Jam. See <a href=
       "../engine/index.html">$boost_build_root/engine/index.html</a> for
@@ -131,8 +131,13 @@ <h2><a name="sec-intro">Introduction for users</a></h2>
     <p>Examples:</p>
 
 <pre class="code">
-python test_all.py
-python generators_test.py
+./test_all.py
+./generators_test.py
+</pre>
+or
+<pre class="code">
+python3 test_all.py
+python3 generators_test.py
 </pre>
 
     <p>If everything is OK, you will see a list of passed tests. Otherwise, a
@@ -144,8 +149,8 @@ <h3><a name="sec-command-line-options">Command line options</a></h3>
     you can specify a specific one on the command line:</p>
 
 <pre class="code">
-python test_all.py borland
-python generators_test.py msvc-7.1
+python3 test_all.py borland
+python3 generators_test.py msvc-7.1
 </pre>
 
     <p>Other test script flags you can specify on the command line are:</p>
@@ -173,7 +178,7 @@ <h2><a name="sec-developers">Introduction for developers</a></h2>
 
     <ul>
       <li>For an interpreted language like Jam, without any static checks,
-      testing is simply the only sefeguard we can have.</li>
+      testing is simply the only safeguard we can have.</li>
 
       <li>Good tests allow us to change internal design much more safely, and we
       have not gotten everything nailed down yet.</li>