Fix up examples of sh/ksh PATH environment variable definition.

doc/src/sgml/environ.sgml

@@ -32,8 +32,8 @@ set path = ( /usr/local/pgsql/bin path )
      a  variant  of  the  Bourne  shell, such as <Application>sh</Application>, <Application>ksh</Application>, or
      <Application>bash</Application>, then you would add
 <ProgramListing>
-PATH=/usr/local/pgsql/bin PATH
-export PATH
+$ PATH=/usr/local/pgsql/bin:$PATH
+$ export PATH
 </ProgramListing>
      to the <FileName>.profile</FileName> file in your home directory.
      From now on, we will assume that  you  have  added  the

doc/src/sgml/runtime.sgml

@@ -62,7 +62,7 @@ set path = ( /usr/local/pgsql/bin path )
      a  variant  of  the  Bourne  shell, such as sh, ksh, or
      bash, then you would add
 <ProgramListing>
-PATH=/usr/local/pgsql/bin PATH
+PATH=/usr/local/pgsql/bin:$PATH
 export PATH
 </ProgramListing>
      to the .profile file in your home directory.

doc/src/sgml/start.sgml

@@ -67,7 +67,7 @@ of a client application is the interactive monitor <Application>psql</Applicatio
      a  variant  of  the  Bourne  shell, such as sh, ksh, or
      bash, then you would add
 <ProgramListing>
-% PATH=/usr/local/pgsql/bin PATH
+% PATH=/usr/local/pgsql/bin:$PATH
 % export PATH
 </ProgramListing>
      to the .profile file in your home directory.