Add the --with-install-suffix configure option.

Fix some bugs in the Makefile's install target.
diff --git a/.gitignore b/.gitignore
index 02018fe..35acc25 100644
--- a/.gitignore
+++ b/.gitignore
@@ -8,5 +8,9 @@
 /jemalloc/doc/jemalloc.3
 /jemalloc/lib/
 /jemalloc/Makefile
+/jemalloc/src/internal/jemalloc_internal\.h
+/jemalloc/src/internal/mtrgraph_defs\.h
+/jemalloc/src/internal/mtrplay_defs\.h
+/jemalloc/src/jemalloc\.h
 /jemalloc/src/jemalloc_defs\.h
 /jemalloc/src/*.[od]