fix wording

Author: vladak

threads.tex

@@ -535,7 +535,7 @@
 
 \begin{itemize}
 \item \label{THREAD_SPECIFIC_DATA} Global variables and dynamically
-allocated data is common to all threads.  Thread specific data provides a way to
+allocated data are common to all threads.  Thread specific data provides a way to
 create a global variable per thread.  Note the difference between that and a
 local variable in the thread function -- as you know, in C, the local variable
 is not visible in other functions called from the thread function.  Thread