BuildSystem: Cleanup userspace directory layout

userspace programs are now in userspace/programs
userspace tests are now in userspace/tests

This makes listing userspace projects much cleaner. Libraries were
already separated to their own directory, so other programs should also.

userspace/tests/test-popen/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(test-popen ${SOURCES})
+banan_link_library(test-popen libc)
+
+install(TARGETS test-popen OPTIONAL)

userspace/tests/test-popen/main.cpp

@@ -0,0 +1,30 @@
+#include <stdio.h>
+#include <unistd.h>
+
+int main(int argc, char** argv)
+{
+	if (argc != 2)
+	{
+		fprintf(stderr, "usage: %s COMMAND\n", argv[0]);
+		return 1;
+	}
+
+	FILE* fp = popen(argv[1], "r");
+	if (fp == nullptr)
+	{
+		perror("popen");
+		return 1;
+	}
+
+	char buffer[128];
+	while (fgets(buffer, sizeof(buffer), fp) != NULL)
+		printf("%s", buffer);
+
+	if (pclose(fp) == -1)
+	{
+		perror("pclose");
+		return 1;
+	}
+
+	return 0;
+}