visual*/.gitignore, do not ignore .c and .h files

visualc-shared/.gitignore

@@ -11,5 +11,7 @@
 !/.gitignore
 
 !/*.c
+!/*.h
 !/*.sln
 !/*.vcproj
+!/*.vcxproj

visualc/.gitignore

@@ -9,10 +9,12 @@
 !/include
 
 !/.gitignore
+
 !/how-to-ngspice-vstudio.txt
 !/visualc/fftw3/fftw-*/README-ngspice.txt
 
 !/*.c
+!/*.h
 !/*.sln
 !/*.vcproj
 !/*.vcxproj