XFce 4.4 beta 2 - problem with plugins

[Przemek Szalko]

Hello!

I've just installed new XFce 4.4 beta 2 on my system (Slackware 10.2)
- works great!
But now, when I'm installing plugins, I've some strange errors in
couple of them.

For example, when compiling xfce4-battery-plugin (v. 0.3.0):

checking for xfce4-panel-1.0 >= 3.99.2... Package xfce4-panel-1.0 was
not found in the pkg-config search path.
Perhaps you should add the directory containing `xfce4-panel-1.0.pc'
to the PKG_CONFIG_PATH environment variable
No package 'xfce4-panel-1.0' found

configure: error: Library requirements (xfce4-panel-1.0 >= 3.99.2) not
met; consider adjusting the PKG_CONFIG_PATH environment variable if
your libraries are in a nonstandard prefix so pkg-config can find
them.


The problem occurs for:
xfce4-battery-plugin-0.3.0
xfce4-i8k-plugin-0.0.2
xfce4-modemlights-plugin-0.1.1
xfce4-wavelan-plugin-0.4.1
xfce4-netload-plugin-0.3.3

I don't know if it's a problem with plugins or with xfce-beta, so I'm
writing here..
Any suggestions?

Thanks in advance :-)

Przemek Szalko