Clarify the default buffering for open(). (Comment from Andrew Dalke
<dalke@bioreason.com>).
diff --git a/Doc/lib/libfuncs.tex b/Doc/lib/libfuncs.tex
index 8914883..38e073f 100644
--- a/Doc/lib/libfuncs.tex
+++ b/Doc/lib/libfuncs.tex
@@ -406,7 +406,7 @@
positive value means use a buffer of (approximately) that size. A
negative \var{bufsize} means to use the system default, which is
usually line buffered for for tty devices and fully buffered for other
-files.%
+files. If omitted, the system default is used.%
\footnote{Specifying a buffer size currently has no effect on systems
that don't have \cfunction{setvbuf()}. The interface to specify the buffer
size is not done using a method that calls \cfunction{setvbuf()}, because