bug#34924: Default _SOURCES fails when the target contains dots

[Дилян Палаузов]

Hello,

I expect that the line

a_b_d_e_f_g_SOURCES = a/b/d-e-f.g.c

to be superflous, as this is a “Default _SOURCE”, but `make` fails with

make[1]: *** No rule to make target 'a/b/d-e-f.c', needed by 
'a/b/d_e_f_g-d-e-f.o'.  Stop

g is lost from the tagret.

…_PROGRAMS = a/b/c-e-f.g

Note, that there is a dot before g in both _SOURCES ad _PROGRAMS, but the 
default extension was not changed from .c .

I use Automake 1.16.1.

Regards
  Дилян