Rename package to libmodbus5 to fix lintian warning

Patch provided by Ivo De Decker <Ivo.DeDecker@UGent.be>.
Debian library packaging guide states "The package name should match the
shared library SONAME"
(http://www.netfort.gr.jp/~dancer/column/libpkg-guide/libpkg-guide.html)

debian/control

@@ -6,7 +6,7 @@ Section: libs
 Build-Depends: debhelper (>= 6), cdbs (>= 0.4.43), autotools-dev, libtool, dpkg-dev (>= 1.13.19), asciidoc
 Homepage: http://libmodbus.org/
 
-Package: libmodbus
+Package: libmodbus5
 Section: libs
 Architecture: any
 Depends: ${shlibs:Depends}, ${misc:Depends}
@@ -20,7 +20,7 @@ Description: library for the Modbus protocol
 Package: libmodbus-dev
 Section: libdevel
 Architecture: any
-Depends: libmodbus (= ${binary:Version}), ${shlibs:Depends}, ${misc:Depends}
+Depends: libmodbus5 (= ${binary:Version}), ${shlibs:Depends}, ${misc:Depends}
 Description: library for the Modbus protocol
  A Modbus library written in C, to send/receive data with a device which
  respects the Modbus protocol. This library can use a serial port or an