Fix typos spotted by Kamil Dudka

defensive-coding/en-US/C-Language.xml

@@ -123,7 +123,7 @@
 		  xmlns:xi="http://www.w3.org/2001/XInclude" />
     </example>
     <para>
-      Basic arithmetic operations a commutative, so for bounds checks,
+      Basic arithmetic operations are commutative, so for bounds checks,
       there are two different but mathematically equivalent
       expressions.  Sometimes, one of the expressions results in
       better code because parts of it can be reduced to a constant.

defensive-coding/en-US/Tasks-Processes.xml

@@ -24,7 +24,7 @@
       <para>
 	The configured program name should be an absolute path.  If it
 	is a relative path, the contents of the <envar>PATH</envar>
-	must be obtained in s secure manner (see <xref
+	must be obtained in a secure manner (see <xref
 	linkend="sect-Defensive_Coding-Tasks-secure_getenv"/>).
 	If the <envar>PATH</envar> variable is not set or untrusted,
 	the safe default <literal>/bin:/usr/bin</literal> must be
@@ -290,7 +290,7 @@
     <para>
       At the moment, the parent process should explicitly wait for
       termination of the child process using
-      <function>waitpid</function> or <function>waitpid</function>,
+      <function>waitpid</function> or <function>waitid</function>,
       and hope that the status is not collected by an event loop
       first.
     </para>

defensive-coding/en-US/Tasks-Temporary_Files.xml

@@ -6,7 +6,7 @@
   <para>
     In this chapter, we describe how to create temporary files and
     directories, how to remove them, and how to work with programs
-    which do not create files in ways that a safe with a shared
+    which do not create files in ways that are safe with a shared
     directory for temporary files.  General file system manipulation
     is treated in a separate chapter, <xref
     linkend="chap-Defensive_Coding-Tasks-File_System"/>.