$(top_srcdir)/uim directory contains both libuim core and plugins.
So does $(top_srcdir)/scm directory. I think it's too thick to see through
codes. I suggest them split them into uim,scm and $(top_srcdir)/plugin/$(IMs)/.

If no objection or suggestion are occurred, I tackle them.

e.g)
 libuim core:
   $(top_srcdir)/uim
   $(top_srcdir)/scm
 Anthy plugin:
    $(top_srcdir)/plugin/anthy/anthy.c
    $(top_srcdir)/plugin/anthy/anthy*.scm
 Canna plugin:
    $(top_srcdir)/plugin/canna/canna.c
    $(top_srcdir)/plugin/anthy/canna*.scm
 ...